---
title: "Firewood Cord Calculator: Measure Stack Volume, Face Cords, and the BTU Output Your Wood Actually Delivers"
canonical: "https://theyieldgrid.com/firewood-cord-calculator/"
model_id: "tyg-2454"
model_version: "1.0.0"
last_reviewed: "2026-05-04T12:54:04"
reviewed_by: "Umer Hayiat"
---

# Firewood Cord Calculator: Measure Stack Volume, Face Cords, and the BTU Output Your Wood Actually Delivers

> Canonical calculator: [https://theyieldgrid.com/firewood-cord-calculator/](https://theyieldgrid.com/firewood-cord-calculator/)

## What this calculator does

Home - Free Gardening Calculators & Tools - Firewood Cord Calculator: Measure Stack Volume, Face Cords, and the BTU Output Your Wood Actually Delivers Buying or cutting firewood by the “cord” sounds straightforward until the stack arrives and no one agrees on what a cord is. A full cord is a defined unit of 128 cubic feet, but what gets sold, stacked, and burned is almost never a full cord. Log length, stacking height, and whether the seller means a full cord or a face cord all change the math before a single log hits the firebox. Add moisture content to that equation and the BTU deficit between what wood could deliver and what it actually delivers in your stove can be staggering.

## Inputs

| Input | ID | Type | Unit | Range or choices | Required |
|---|---|---|---|---|---|
| Stack Length * | `fwcalc_length` | number | feet | 0.1 to 500 | Yes |
| Stack Height * | `fwcalc_height` | number | standard cord = 4 ft | 0.1 to 20 | Yes |
| Log Length * | `fwcalc_loglen` | number | standard = 16 in | 6 to 48 | Yes |
| Moisture Content (%) * | `fwcalc_moisture` | number | % | 5 to 80 | Yes |
| Wood Species * | `fwcalc_species` | select | BTU | — Select species — = ``; Red Oak — 24.0 million BTU/cord (Excellent) = `oak`; White Ash — 20.0 million BTU/cord (Very Good) = `ash`; Pine — 14.3 million BTU/cord (Good starter) = `pine` | Yes |

## Outputs

| Output ID | Default state |
|---|---|
| `fwcalc_length_err` | Required |
| `fwcalc_height_err` | Required |
| `fwcalc_loglen_err` | Required |
| `fwcalc_moisture_err` | Required |
| `fwcalc_species_err` | Required |
| `fwcalc_results_panel` | Your Results Firewood cord volume & actual BTU output for your stack Full Cords — cords — Cubic Feet (stack volume) — Face Cords (16-inch logs) — Million BTU (actual output) BTU Efficiency vs. Ideal Dry Cord — Ideal 25% Warnings & Standards Check Species & Moisture Reference Table Species Dry BTU/cord At 15% MC At 25% MC At 35% MC Rating Recommended Tools for Your Stack |
| `fwcalcout_primary` | — |
| `fwcalcout_volume` | — |
| `fwcalcout_face` | — |
| `fwcalcout_btu` | — |
| `fwcalcout_warnings_box` | Warnings & Standards Check |
| `fwcalcout_warnings_title` | Warnings & Standards Check |
| `fwcalcout_warnings_list` |  |

## Formula and method

How moisture content directly reduces BTU output through the calculator’s precise penalty bands. Show the calculation steps Step 1: Stack Volume in Cubic Feet Volume (ft³) = Stack Length (ft) x Stack Height (ft) x (Log Length (in) / 12) The log length is converted from inches to feet by dividing by 12. This gives the depth dimension of the stack in feet. Multiplying all three dimensions produces total stack volume in cubic feet. Step 2: Full Cords and Face Cords Full Cords = Volume (ft³) / 128 A full cord equals 4 ft x 4 ft x 8 ft = 128 cubic feet by legal definition in most U.S. states. Face Cords are calculated as: Full Cords x (48 / Log Length in inches). This expresses how many face-cord-equivalents exist using 16-inch standard logs as the reference depth. If your logs are 16 inches, one face cord = one-third of a full cord. Step 3: Moisture Factor The moisture factor adjusts the base BTU rating downward as moisture content rises. The formula uses three bands: If MC is 15% or below: factor = 1.0 – (MC – 15) x 0.004 (minor reduction, approaching 1.0 at 15%) If MC is between 15% and 20%: same formula, smooth linear slope If MC is above 20% and up to 30%: factor = 0.85 – (MC – 20) x 0.025 (steeper slope, significant BTU loss) If MC exceeds 30%: factor = 0.60 – (MC – 30) x 0.012 (severe loss, floor of 0.20) The factor floor of 0.20 prevents the output from reaching zero, acknowledging that even very wet wood produces some heat. Rounding: all output values are rounded to two decimal places. Volume uses one decimal place. Step 4: Actual BTU Actual BTU (M BTU) = Full Cords x Species Base BTU x Moisture Factor Species base BTU values used: Red Oak = 24.0 M BTU/cord, White Ash = 20.0 M BTU/cord, Pine = 14.3 M BTU/cord. These are midpoint figures from USDA Forest Products Laboratory published ranges for air-dry wood at approximately 15% moisture content. BTU Efficiency Gauge Efficiency = (Actual BTU / (Full Cords x Species BTU x Moisture Factor at 15%)) x 100 This compares your moisture-adjusted output to what the same stack would produce at ideal 15% MC, expressed as a percentage. Assumptions and Limits BTU-per-cord figures are midpoint averages from published USDA Forest Products Laboratory data for air-dry wood. Actual values vary by tree age, soil conditions, heartwood-to-sapwood ratio, and splitting quality. Stack volume assumes tight, straight stacking. Irregular, crossed, or gapped stacking can reduce actual wood content by 15 to 25%, meaning the calculator overestimates volume for loosely stacked piles. The moisture factor is a thermodynamic approximation. Real-world BTU loss also depends on stove combustion efficiency (modern EPA-certified stoves recover more), flue draw, and air supply settings. Moisture content entered must come from a pin-type meter reading on a freshly split log face. Surface readings, especially on split wood that has air-dried on the outside, will read lower than the interior and lead the calculator to overestimate BTU output. Face cord output is calculated using 16-inch logs as the reference denominator for “standard” face cord depth. If you use a different log length, the face cord count reflects your actual log depth, not the traditional 16-inch convention. Creosote risk ratings in the widget are derived from the NFPA 211 standard and EPA wood-burning guidance, which cite 25% MC as the threshold above which low flue temperatures and condensation risk increase significantly. The calculator does not account for bark-on versus bark-off logs. Bark adds volume without adding proportional BTU content; bark-heavy stacks will produce slightly less heat than the species rating suggests. Altitude affects combustion completeness. At elevations above 5,000 feet, wood stoves may need draft adjustments; the BTU output figures assume sea-level combustion conditions.

## Verified worked examples

### Scenario 1: Standard 8×4 Stack of Seasoned Red Oak, 16-Inch Logs

Stack Length: 8 ft Stack Height: 4 ft Log Length: 16 in Moisture Content: 15% Species: Red Oak (24.0 M BTU per full cord dry) Volume = 8 x 4 x (16/12) = 42.67 cubic feet. Full Cords = 42.67 / 128 = 0.33 cords. Moisture factor at 15% = 1.0 – (15 – 15) x 0.004 = 1.0. Actual BTU = 0.33 x 24.0 x 1.0 = 7.93 million BTU . Result: 0.33 full cords delivering 7.93 million BTU at 100% moisture efficiency. This is a textbook face cord of seasoned oak at peak performance. At this moisture level, essentially no BTUs are lost to water evaporation before combustion.

### Scenario 2: Large 16×4 Stack of Green Red Oak, 16-Inch Logs

Stack Length: 16 ft Stack Height: 4 ft Log Length: 16 in Moisture Content: 30% Species: Red Oak (24.0 M BTU per full cord dry) Volume = 16 x 4 x (16/12) = 85.33 cubic feet. Full Cords = 85.33 / 128 = 0.667 cords. Moisture factor at 30% = 0.85 – (30 – 20) x 0.025 = 0.85 – 0.25 = 0.60. Actual BTU = 0.667 x 24.0 x 0.60 = 9.6 million BTU . Result: 0.67 full cords delivering only 9.6 million BTU — 40% of maximum potential output lost to moisture. This same stack, if properly seasoned to 15% MC, would yield approximately 16.0 million BTU. The difference represents enough heat to matter significantly in a cold winter month, and the lost energy exits the flue as steam and precursor compounds that deposit as creosote.

### Scenario 3: 8×4 Stack of Dry Pine, 24-Inch Logs

Stack Length: 8 ft Stack Height: 4 ft Log Length: 24 in Moisture Content: 18% Species: Pine (14.3 M BTU per full cord dry) Volume = 8 x 4 x (24/12) = 64.0 cubic feet. Full Cords = 64.0 / 128 = 0.50 cords. Face Cords (16-in equivalent) = 0.50 x (48/24) = 1.0 face cord. Moisture factor at 18% = 1.0 – (18 – 15) x 0.004 = 1.0 – 0.012 = 0.988. Actual BTU = 0.50 x 14.3 x 0.988 = 7.07 million BTU . Result: 0.50 full cords of dry pine delivering 7.07 million BTU. At 18% MC, pine performs close to its rated output. The species limitation is the base BTU figure, not moisture in this case. Dry pine burns fast and hot — useful for quick heat or kindling — but its lower density means you burn through volume faster than hardwood at the same BTU demand.

## Assumptions

Stack Length: 8 ft Stack Height: 4 ft Log Length: 16 in Moisture Content: 15% Species: Red Oak (24.0 M BTU per full cord dry) Volume = 8 x 4 x (16/12) = 42.67 cubic feet. Full Cords = 42.67 / 128 = 0.33 cords. Moisture factor at 15% = 1.0 – (15 – 15) x 0.004 = 1.0. Actual BTU = 0.33 x 24.0 x 1.0 = 7.93 million BTU . Result: 0.33 full cords delivering 7.93 million BTU at 100% moisture efficiency. This is a textbook face cord of seasoned oak at peak performance. At this moisture level, essentially no BTUs are lost to water evaporation before combustion. How moisture content directly reduces BTU output through the calculator’s precise penalty bands. Show the calculation steps Step 1: Stack Volume in Cubic Feet Volume (ft³) = Stack Length (ft) x Stack Height (ft) x (Log Length (in) / 12) The log length is converted from inches to feet by dividing by 12. This gives the depth dimension of the stack in feet. Multiplying all three dimensions produces total stack volume in cubic feet. Step 2: Full Cords and Face Cords Full Cords = Volume (ft³) / 128 A full cord equals 4 ft x 4 ft x 8 ft = 128 cubic feet by legal definition in most U.S. states. Face Cords are calculated as: Full Cords x (48 / Log Length in inches). This expresses how many face-cord-equivalents exist using 16-inch standard logs as the reference depth. If your logs are 16 inches, one face cord = one-third of a full cord. Step 3: Moisture Factor The moisture factor adjusts the base BTU rating downward as moisture content rises. The formula uses three bands: If MC is 15% or below: factor = 1.0 – (MC – 15) x 0.004 (minor reduction, approaching 1.0 at 15%) If MC is between 15% and 20%: same formula, smooth linear slope If MC is above 20% and up to 30%: factor = 0.85 – (MC – 20) x 0.025 (steeper slope, significant BTU loss) If MC exceeds 30%: factor = 0.60 – (MC – 30) x 0.012 (severe loss, floor of 0.20) The factor floor of 0.20 prevents the output from reaching zero, acknowledging that even very wet wood produces some heat. Rounding: all output values are rounded to two decimal places. Volume uses one decimal place. Step 4: Actual BTU Actual BTU (M BTU) = Full Cords x Species Base BTU x Moisture Factor Species base BTU values used: Red Oak = 24.0 M BTU/cord, White Ash = 20.0 M BTU/cord, Pine = 14.3 M BTU/cord. These are midpoint figures from USDA Forest Products Laboratory published ranges for air-dry wood at approximately 15% moisture content. BTU Efficiency Gauge Efficiency = (Actual BTU / (Full Cords x Species BTU x Moisture Factor at 15%)) x 100 This compares your moisture-adjusted output to what the same stack would produce at ideal 15% MC, expressed as a percentage. Assumptions and Limits BTU-per-cord figures are midpoint averages from published USDA Forest Products Laboratory data for air-dry wood. Actual values vary by tree age, soil conditions, heartwood-to-sapwood ratio, and splitting quality. Stack volume assumes tight, straight stacking. Irregular, crossed, or gapped stacking can reduce actual wood content by 15 to 25%, meaning the calculator overestimates volume for loosely stacked piles. The moisture factor is a thermodynamic approximation. Real-world BTU loss also depends on stove combustion efficiency (modern EPA-certified stoves recover more), flue draw, and air supply settings. Moisture content entered must come from a pin-type meter reading on a freshly split log face. Surface readings, especially on split wood that has air-dried on the outside, will read lower than the interior and lead the calculator to overestimate BTU output. Face cord output is calculated using 16-inch logs as the reference denominator for “standard” face cord depth. If you use a different log length, the face cord count reflects your actual log depth, not the traditional 16-inch convention. Creosote risk ratings in the widget are derived from the NFPA 211 standard and EPA wood-burning guidance, which cite 25% MC as the threshold above which low flue temperatures and condensation risk increase significantly. The calculator does not account for bark-on versus bark-off logs. Bark adds volume without adding proportional BTU content; bark-heavy stacks will produce slightly less heat than the species rating suggests. Altitude affects combustion completeness. At elevations above 5,000 feet, wood stoves may need draft adjustments; the BTU output figures assume sea-level combustion conditions. BTU-per-cord figures are midpoint averages from published USDA Forest Products Laboratory data for air-dry wood. Actual values vary by tree age, soil conditions, heartwood-to-sapwood ratio, and splitting quality. Stack volume assumes tight, straight stacking. Irregular, crossed, or gapped stacking can reduce actual wood content by 15 to 25%, meaning the calculator overestimates volume for loosely stacked piles. The moisture factor is a thermodynamic approximation. Real-world BTU loss also depends on stove combustion efficiency (modern EPA-certified stoves recover more), flue draw, and air supply settings. Moisture content entered must come from a pin-type meter reading on a freshly split log face. Surface readings, especially on split wood that has air-dried on the outside, will read lower than the interior and lead the calculator to overestimate BTU output. Face cord output is calculated using 16-inch logs as the reference denominator for “standard” face cord depth. If you use a different log length, the face cord count reflects your actual log depth, not the traditional 16-inch convention. Creosote risk ratings in the widget are derived from the NFPA 211 standard and EPA wood-burning guidance, which cite 25% MC as the threshold above which low flue temperatures and condensation risk increase significantly. The calculator does not account for bark-on versus bark-off logs. Bark adds volume without adding proportional BTU content; bark-heavy stacks will produce slightly less heat than the species rating suggests. Altitude affects combustion completeness. At elevations above 5,000 feet, wood stoves may need draft adjustments; the BTU output figures assume sea-level combustion conditions. Critical Warnings The Creosote Threshold: Wood above 25% moisture content burns at temperatures too low to exhaust flue gases cleanly. The resulting steam, laced with volatile compounds, condenses on chimney walls as creosote. At 30% MC or higher, this process is rapid. Stage 3 glazed creosote, the type produced by sustained wet-wood burning, is highly flammable and extremely difficult to remove. NFPA 211 is explicit: if you are burning unseasoned wood regularly, your flue must be inspected and swept before each heating season. The Face Cord Trap: Most residential firewood is sold as a “face cord” or “rick,” not a full cord. A face cord stacked with 16-inch logs holds one-third the wood of a full cord by volume. A face cord with 24-inch logs holds half a full cord. Sellers who price by the face cord without specifying log length are selling an ambiguous product. Run your numbers before purchasing — a face cord at full-cord pricing is not a deal; it is a unit mismatch. BTU Claims Without Moisture Context are Meaningless: A cord of Red Oak rated at 24 million BTU assumes dry wood at approximately 15% MC. That same cord at 30% MC delivers closer to 14.4 million BTU. Firewood sellers who cite species BTU ratings without discussing moisture are quoting theoretical maximums, not what you will get from the stack. Surface Meter Readings Lie: A pin-type moisture meter pressed against the outer face of a split log that has been air-drying for two weeks will read lower than the interior. Always split a fresh log and measure immediately from the newly exposed center. This is the reading the calculator needs to produce an accurate BTU estimate. Minimum Standards Moisture content at or below 20% before burning in a wood stove or fireplace insert, consistent with EPA and most state air quality guidelines for residential wood burning. Annual chimney inspection and sweeping before each heating season, per NFPA 211, especially if any green or unseasoned wood was burned in the prior season. A full cord is legally defined as 128 cubic feet in stacked, 4-foot logs. Any unit smaller than this sold as a “cord” may violate consumer protection weights-and-measures laws in your state. When in doubt, request dimensions in writing. Firewood should be stored off the ground on a rack, covered on top but open on the sides, for a minimum of 6 months for softwoods and 12 months for dense hardwoods like oak, to reach acceptable moisture levels without a kiln. Competitor Trap: Most firewood BTU comparison articles rank species by million BTU per cord and stop there. They do not calculate what those numbers mean at the moisture levels typical of wood sold commercially in the fall, when a large percentage of firewood on the market has been cut within the same growing season. An article that tells you Red Oak delivers 24 million BTU per cord without explaining that green oak at 35% MC delivers closer to 11 million BTU per cord is giving you half the information needed to make a real decision. For anyone heating a barn or outbuilding, where combustion appliances are often running harder and chimneys are less frequently swept, the moisture penalty is not a footnote — it is the central variable. The barn ventilation calculator is a useful companion for homesteaders sizing heating systems for enclosed animal spaces, where flue gas management and combustion air interact with ventilation requirements. Homesteaders planning their total winter fuel budget alongside hay and feed costs will find the winter cattle feed calculator a useful companion for projecting all cold-weather operational expenses together rather than treating firewood and livestock feed as separate line items. Moisture content at or below 20% before burning in a wood stove or fireplace insert, consistent with EPA and most state air quality guidelines for residential wood burning. Annual chimney inspection and sweeping before each heating season, per NFPA 211, especially if any green or unseasoned wood was burned in the prior season. A full cord is legally defined as 128 cubic feet in stacked, 4-foot logs. Any unit smaller than this sold as a “cord” may violate consumer protection weights-and-measures laws in your state. When in doubt, request dimensions in writing. Firewood should be stored off the ground on a rack, covered on top but open on the sides, for a minimum of 6 months for softwoods and 12 months for dense hardwoods like oak, to reach acceptable moisture levels without a kiln. Competitor Trap: Most firewood BTU comparison articles rank species by million BTU per cord and stop there. They do not calculate what those numbers mean at the moisture levels typical of wood sold commercially in the fall, when a large percentage of firewood on the market has been cut within the same growing season. An article that tells you Red Oak delivers 24 million BTU per cord without explaining that green oak at 35% MC delivers closer to 11 million BTU per cord is giving you half the information needed to make a real decision. For anyone heating a barn or outbuilding, where combustion appliances are often running harder and chimneys are less frequently swept, the moisture penalty is not a footnote — it is the central variable. The barn ventilation calculator is a useful companion for homesteaders sizing heating systems for enclosed animal spaces, where flue gas management and combustion air interact with ventilation requirements. Homesteaders planning their total winter fuel budget alongside hay and feed costs will find the winter cattle feed calculator a useful companion for projecting all cold-weather operational expenses together rather than treating firewood and livestock feed as separate line items.

## Limitations and safety

BTU-per-cord figures are midpoint averages from published USDA Forest Products Laboratory data for air-dry wood. Actual values vary by tree age, soil conditions, heartwood-to-sapwood ratio, and splitting quality. Stack volume assumes tight, straight stacking. Irregular, crossed, or gapped stacking can reduce actual wood content by 15 to 25%, meaning the calculator overestimates volume for loosely stacked piles. The moisture factor is a thermodynamic approximation. Real-world BTU loss also depends on stove combustion efficiency (modern EPA-certified stoves recover more), flue draw, and air supply settings. Moisture content entered must come from a pin-type meter reading on a freshly split log face. Surface readings, especially on split wood that has air-dried on the outside, will read lower than the interior and lead the calculator to overestimate BTU output. Face cord output is calculated using 16-inch logs as the reference denominator for “standard” face cord depth. If you use a different log length, the face cord count reflects your actual log depth, not the traditional 16-inch convention. Creosote risk ratings in the widget are derived from the NFPA 211 standard and EPA wood-burning guidance, which cite 25% MC as the threshold above which low flue temperatures and condensation risk increase significantly. The calculator does not account for bark-on versus bark-off logs. Bark adds volume without adding proportional BTU content; bark-heavy stacks will produce slightly less heat than the species rating suggests. Altitude affects combustion completeness. At elevations above 5,000 feet, wood stoves may need draft adjustments; the BTU output figures assume sea-level combustion conditions. Critical Warnings The Creosote Threshold: Wood above 25% moisture content burns at temperatures too low to exhaust flue gases cleanly. The resulting steam, laced with volatile compounds, condenses on chimney walls as creosote. At 30% MC or higher, this process is rapid. Stage 3 glazed creosote, the type produced by sustained wet-wood burning, is highly flammable and extremely difficult to remove. NFPA 211 is explicit: if you are burning unseasoned wood regularly, your flue must be inspected and swept before each heating season. The Face Cord Trap: Most residential firewood is sold as a “face cord” or “rick,” not a full cord. A face cord stacked with 16-inch logs holds one-third the wood of a full cord by volume. A face cord with 24-inch logs holds half a full cord. Sellers who price by the face cord without specifying log length are selling an ambiguous product. Run your numbers before purchasing — a face cord at full-cord pricing is not a deal; it is a unit mismatch. BTU Claims Without Moisture Context are Meaningless: A cord of Red Oak rated at 24 million BTU assumes dry wood at approximately 15% MC. That same cord at 30% MC delivers closer to 14.4 million BTU. Firewood sellers who cite species BTU ratings without discussing moisture are quoting theoretical maximums, not what you will get from the stack. Surface Meter Readings Lie: A pin-type moisture meter pressed against the outer face of a split log that has been air-drying for two weeks will read lower than the interior. Always split a fresh log and measure immediately from the newly exposed center. This is the reading the calculator needs to produce an accurate BTU estimate. Minimum Standards Moisture content at or below 20% before burning in a wood stove or fireplace insert, consistent with EPA and most state air quality guidelines for residential wood burning. Annual chimney inspection and sweeping before each heating season, per NFPA 211, especially if any green or unseasoned wood was burned in the prior season. A full cord is legally defined as 128 cubic feet in stacked, 4-foot logs. Any unit smaller than this sold as a “cord” may violate consumer protection weights-and-measures laws in your state. When in doubt, request dimensions in writing. Firewood should be stored off the ground on a rack, covered on top but open on the sides, for a minimum of 6 months for softwoods and 12 months for dense hardwoods like oak, to reach acceptable moisture levels without a kiln. Competitor Trap: Most firewood BTU comparison articles rank species by million BTU per cord and stop there. They do not calculate what those numbers mean at the moisture levels typical of wood sold commercially in the fall, when a large percentage of firewood on the market has been cut within the same growing season. An article that tells you Red Oak delivers 24 million BTU per cord without explaining that green oak at 35% MC delivers closer to 11 million BTU per cord is giving you half the information needed to make a real decision. For anyone heating a barn or outbuilding, where combustion appliances are often running harder and chimneys are less frequently swept, the moisture penalty is not a footnote — it is the central variable. The barn ventilation calculator is a useful companion for homesteaders sizing heating systems for enclosed animal spaces, where flue gas management and combustion air interact with ventilation requirements. Homesteaders planning their total winter fuel budget alongside hay and feed costs will find the winter cattle feed calculator a useful companion for projecting all cold-weather operational expenses together rather than treating firewood and livestock feed as separate line items.

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## Provenance

- Model ID: `tyg-2454`
- Model version: `1.0.0`
- Reviewed by: Umer Hayiat
- Page modified: 2026-05-04T12:54:04
- Runtime SHA-256: `e98ef0d38caed49f38575b03a0f977993d9fad17964dfb4c1aa034ca6a05eae2`

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