---
title: "CO2 Calculator: Predict Tank Duration Before Your Regulator Setting Drains It Early"
canonical: "https://theyieldgrid.com/co2-calculator/"
model_id: "tyg-692"
model_version: "1.0.0"
last_reviewed: "2026-08-20T09:58:54"
reviewed_by: "Umer Hayiat"
---

# CO2 Calculator: Predict Tank Duration Before Your Regulator Setting Drains It Early

> Canonical calculator: [https://theyieldgrid.com/co2-calculator/](https://theyieldgrid.com/co2-calculator/)

## What this calculator does

Home - Free Gardening Calculators & Tools - CO2 Calculator: Predict Tank Duration Before Your Regulator Setting Drains It Early Running out of CO2 mid-cycle is not a minor inconvenience -- it is a measurable setback for any crop that depends on enriched atmospheres to hit yield targets. The variable that most growers underestimate is not tank size or flow rate in isolation; it is the interaction between flow rate and duty cycle. A regulator set to 1 SCFH running 30 minutes per hour consumes exactly half as much gas as the same regulator running continuously -- yet the overwhelming majority of online duration estimates treat CO2 as if it flows 24/7.

## Inputs

| Input | ID | Type | Unit | Range or choices | Required |
|---|---|---|---|---|---|
| Tank Size | `co2tank_size` | select |  | — Select tank size — = ``; 5 lb tank = `5`; 10 lb tank = `10`; 20 lb tank = `20`; 50 lb tank = `50`; Custom weight… = `custom` | Yes |
| Custom Tank Weight (lbs) | `co2tank_custom` | number | lbs | 1 to 300 | No |
| Flow Rate (SCFH) | `co2tank_flow` | number |  | 0.1 to 50 | No |
| Burn Time (mins active / hr) | `co2tank_burn` | number | hour | 1 to 60 | No |
| Daily Use Hours | `co2tank_daily` | number | Hours | 1 to 24 | No |

## Outputs

| Output ID | Default state |
|---|---|
| `co2tank_results` | Estimated Tank Duration hours Tank Life Short (72 hrs) Warnings & Standards Reference: Common Tank Durations at Your Flow Settings Tank Size Gas Volume (cu ft) Usage/Hr (cu ft) Duration (hrs) @ 12 hrs/day How this calculator works 1 Gas Volume — Convert tank weight to cubic feet of CO2 Gas Volume (cu ft) = Tank Weight (lbs) × 8.74 CO2 expands ~8.74 cu ft per pound at standard temperature and pressure (STP) 2 Usage Per Hour — Actual CO2 consumed per active hou |
| `co2tank_out_primary` |  |

## Formula and method

This tool calculates the real-world expansion of liquid CO2 into gas based on your specific regulator duty cycle. Show the calculation steps Step 1 -- Convert tank weight to gas volume: CO2 expands at a ratio of approximately 8.74 cubic feet per pound at standard temperature and pressure (70 degrees F / 21 degrees C, 1 atmosphere). Multiply tank weight in pounds by 8.74 to get total available gas in cubic feet. Gas Volume (cu ft) = Tank Weight (lbs) x 8.74 Step 2 -- Calculate actual usage per active hour: The burn time input converts a timer's duty cycle into a fractional hour. Dividing burn minutes by 60 gives the fraction of each hour the regulator is open. Multiply that fraction by the flow rate to get real consumption per active hour. Usage per Hour (cu ft) = Flow Rate (SCFH) x (Burn Minutes / 60) Step 3 -- Calculate tank duration in active hours: Divide total gas volume by usage per active hour to get the number of hours the tank will supply CO2 while the system is running. Duration (hrs) = Gas Volume (cu ft) / Usage per Hour (cu ft) Step 4 -- Convert to calendar days: Divide total active hours by daily use hours to translate the duration into a refill schedule expressed in days. Days = Duration (hrs) / Daily Use Hours (hrs/day) Rounding: All intermediate values are computed in full precision. The primary output is rounded to one decimal place. Reference table values are rounded to one decimal place for readability. Assumptions and Limits The 8.74 cu ft/lb expansion factor applies at 70 degrees F and 1 atmosphere. Cold storage environments (below 50 degrees F) reduce actual expansion, meaning the tank may deliver slightly less gas than calculated. Flow rate is assumed to be constant and stable at the regulator's set value throughout the tank's life. In practice, flow rate can drop slightly as tank pressure decreases below approximately 500 PSI. Tank fill is assumed to be 100% at the weight entered. If entering a partially used tank, weigh the cylinder and subtract the tare weight stamped on the collar before entering the value. No leaks, line losses, or pressure drops are modeled. A faulty check valve or loose fitting can drain a tank significantly faster than calculated. The calculator does not model room volume, air exchange rate, or CO2 concentration (PPM). It computes gas supply duration only, not whether that gas is sufficient to reach a target concentration. Maximum supported inputs: 300 lbs tank weight, 50 SCFH flow rate, 60 minutes burn time. Values outside these ranges are blocked by inline validation. Results are estimates. Real-world duration typically varies plus or minus 10 to 15 percent depending on tank age, ambient temperature, and regulator calibration drift.

## Verified worked examples

### Example 1: Small Grow Tent with a 20 lb Tank

Tank size: 20 lb Flow rate: 0.5 SCFH Burn time: 15 minutes per hour Daily use: 12 hours Gas volume: 20 x 8.74 = 174.8 cu ft. Usage per active hour: 0.5 x (15 / 60) = 0.125 cu ft. Duration: 174.8 / 0.125 = 1,398 hours . Result: At 12 hours per day, this tank lasts approximately 116 days -- nearly four months without a refill. This scenario reflects a conservative timer setting that preserves gas effectively for a single-tent operation.

### Example 2: Mid-Scale Greenhouse, 50 lb Tank

Tank size: 50 lb Flow rate: 1.5 SCFH Burn time: 20 minutes per hour Daily use: 16 hours Gas volume: 50 x 8.74 = 437.0 cu ft. Usage per active hour: 1.5 x (20 / 60) = 0.5 cu ft. Duration: 437.0 / 0.5 = 874 hours . Result: At 16 hours per day, this configuration yields approximately 54.6 days. A 50 lb tank is a workable solution for this setup, though a bimonthly exchange schedule should be planned in advance.

### Example 3: Aggressive Enrichment, 20 lb Tank

Tank size: 20 lb Flow rate: 2.0 SCFH Burn time: 30 minutes per hour Daily use: 18 hours Gas volume: 20 x 8.74 = 174.8 cu ft. Usage per active hour: 2.0 x (30 / 60) = 1.0 cu ft. Duration: 174.8 / 1.0 = 174.8 hours . Result: At 18 hours per day, this tank empties in approximately 9.7 days. High flow rates with long duty cycles consume a 20 lb tank faster than most growers expect. Stepping up to a 50 lb cylinder, or reducing the duty cycle, would extend intervals significantly.

## Assumptions

This tool calculates the real-world expansion of liquid CO2 into gas based on your specific regulator duty cycle. Show the calculation steps Step 1 -- Convert tank weight to gas volume: CO2 expands at a ratio of approximately 8.74 cubic feet per pound at standard temperature and pressure (70 degrees F / 21 degrees C, 1 atmosphere). Multiply tank weight in pounds by 8.74 to get total available gas in cubic feet. Gas Volume (cu ft) = Tank Weight (lbs) x 8.74 Step 2 -- Calculate actual usage per active hour: The burn time input converts a timer's duty cycle into a fractional hour. Dividing burn minutes by 60 gives the fraction of each hour the regulator is open. Multiply that fraction by the flow rate to get real consumption per active hour. Usage per Hour (cu ft) = Flow Rate (SCFH) x (Burn Minutes / 60) Step 3 -- Calculate tank duration in active hours: Divide total gas volume by usage per active hour to get the number of hours the tank will supply CO2 while the system is running. Duration (hrs) = Gas Volume (cu ft) / Usage per Hour (cu ft) Step 4 -- Convert to calendar days: Divide total active hours by daily use hours to translate the duration into a refill schedule expressed in days. Days = Duration (hrs) / Daily Use Hours (hrs/day) Rounding: All intermediate values are computed in full precision. The primary output is rounded to one decimal place. Reference table values are rounded to one decimal place for readability. Assumptions and Limits The 8.74 cu ft/lb expansion factor applies at 70 degrees F and 1 atmosphere. Cold storage environments (below 50 degrees F) reduce actual expansion, meaning the tank may deliver slightly less gas than calculated. Flow rate is assumed to be constant and stable at the regulator's set value throughout the tank's life. In practice, flow rate can drop slightly as tank pressure decreases below approximately 500 PSI. Tank fill is assumed to be 100% at the weight entered. If entering a partially used tank, weigh the cylinder and subtract the tare weight stamped on the collar before entering the value. No leaks, line losses, or pressure drops are modeled. A faulty check valve or loose fitting can drain a tank significantly faster than calculated. The calculator does not model room volume, air exchange rate, or CO2 concentration (PPM). It computes gas supply duration only, not whether that gas is sufficient to reach a target concentration. Maximum supported inputs: 300 lbs tank weight, 50 SCFH flow rate, 60 minutes burn time. Values outside these ranges are blocked by inline validation. Results are estimates. Real-world duration typically varies plus or minus 10 to 15 percent depending on tank age, ambient temperature, and regulator calibration drift. The 8.74 cu ft/lb expansion factor applies at 70 degrees F and 1 atmosphere. Cold storage environments (below 50 degrees F) reduce actual expansion, meaning the tank may deliver slightly less gas than calculated. Flow rate is assumed to be constant and stable at the regulator's set value throughout the tank's life. In practice, flow rate can drop slightly as tank pressure decreases below approximately 500 PSI. Tank fill is assumed to be 100% at the weight entered. If entering a partially used tank, weigh the cylinder and subtract the tare weight stamped on the collar before entering the value. No leaks, line losses, or pressure drops are modeled. A faulty check valve or loose fitting can drain a tank significantly faster than calculated. The calculator does not model room volume, air exchange rate, or CO2 concentration (PPM). It computes gas supply duration only, not whether that gas is sufficient to reach a target concentration. Maximum supported inputs: 300 lbs tank weight, 50 SCFH flow rate, 60 minutes burn time. Values outside these ranges are blocked by inline validation. Results are estimates. Real-world duration typically varies plus or minus 10 to 15 percent depending on tank age, ambient temperature, and regulator calibration drift. Critical Warnings The duty cycle is the hidden variable. Entering your flow rate without accounting for burn time produces an estimate that is often 3 to 4 times longer than reality. A regulator set to 1 SCFH running 15 minutes per hour consumes exactly 0.25 cu ft per active hour -- not 1. Every duration estimate that ignores this will be off by the same factor. Flow rate units must match. Regulator gauges in North America are commonly labeled in SCFH, but some imported units display LPM (liters per minute) or CFM (cubic feet per minute). Entering a CFM value as SCFH produces a result 60 times larger than actual. Verify your gauge's unit label before entering any number. Partial tanks produce pro-rated results. A 20 lb cylinder that is only half full contains the equivalent of a 10 lb fill. Always weigh the cylinder and subtract tare weight for mid-cycle calculations. CO2 enrichment without adequate light produces minimal crop benefit. Elevated CO2 increases photosynthesis rates only when light levels are also elevated. Using this DLI calculator alongside CO2 duration planning helps ensure your light and gas schedules are aligned for actual plant response. Minimum Standards For most indoor cannabis and vegetable crops, a target of 1,000 to 1,500 ppm CO2 is standard. A practical midpoint of 1,200 ppm is widely referenced across controlled environment agriculture guidelines. CO2 enrichment is only productive during the photoperiod. Running CO2 during dark hours in a sealed room produces no photosynthetic benefit and wastes supply. Set your daily use hours to match your light-on period. For greenhouse applications where natural CO2 exchange occurs through vents, enrichment is most effective when ventilation is minimized. The greenhouse CO2 calculator accounts for room volume and exchange rate to help size supplementation correctly for non-sealed environments. Competitor Trap: Most CO2 duration calculators on the web use a simplified formula: Gas Volume / Flow Rate. That approach assumes the regulator runs continuously at full flow, 24 hours a day, which is almost never how grow room CO2 systems operate. The result is a duration estimate that overstates actual tank life by a factor proportional to your duty cycle. A timer set to 15 minutes on, 45 minutes off means the true consumption rate is one quarter of the regulator's stated flow. Calculators that omit burn time and daily hours are not calculating your situation -- they are calculating a theoretical maximum that no real installation matches. Tools that also ignore the CO2 burner heat load produced by propane or natural gas CO2 generators miss an additional variable; those systems interact with the CO2 burner heat load in ways that require separate AC or ventilation sizing. For most indoor cannabis and vegetable crops, a target of 1,000 to 1,500 ppm CO2 is standard. A practical midpoint of 1,200 ppm is widely referenced across controlled environment agriculture guidelines. CO2 enrichment is only productive during the photoperiod. Running CO2 during dark hours in a sealed room produces no photosynthetic benefit and wastes supply. Set your daily use hours to match your light-on period. For greenhouse applications where natural CO2 exchange occurs through vents, enrichment is most effective when ventilation is minimized. The greenhouse CO2 calculator accounts for room volume and exchange rate to help size supplementation correctly for non-sealed environments. Competitor Trap: Most CO2 duration calculators on the web use a simplified formula: Gas Volume / Flow Rate. That approach assumes the regulator runs continuously at full flow, 24 hours a day, which is almost never how grow room CO2 systems operate. The result is a duration estimate that overstates actual tank life by a factor proportional to your duty cycle. A timer set to 15 minutes on, 45 minutes off means the true consumption rate is one quarter of the regulator's stated flow. Calculators that omit burn time and daily hours are not calculating your situation -- they are calculating a theoretical maximum that no real installation matches. Tools that also ignore the CO2 burner heat load produced by propane or natural gas CO2 generators miss an additional variable; those systems interact with the CO2 burner heat load in ways that require separate AC or ventilation sizing.

## Limitations and safety

The 8.74 cu ft/lb expansion factor applies at 70 degrees F and 1 atmosphere. Cold storage environments (below 50 degrees F) reduce actual expansion, meaning the tank may deliver slightly less gas than calculated. Flow rate is assumed to be constant and stable at the regulator's set value throughout the tank's life. In practice, flow rate can drop slightly as tank pressure decreases below approximately 500 PSI. Tank fill is assumed to be 100% at the weight entered. If entering a partially used tank, weigh the cylinder and subtract the tare weight stamped on the collar before entering the value. No leaks, line losses, or pressure drops are modeled. A faulty check valve or loose fitting can drain a tank significantly faster than calculated. The calculator does not model room volume, air exchange rate, or CO2 concentration (PPM). It computes gas supply duration only, not whether that gas is sufficient to reach a target concentration. Maximum supported inputs: 300 lbs tank weight, 50 SCFH flow rate, 60 minutes burn time. Values outside these ranges are blocked by inline validation. Results are estimates. Real-world duration typically varies plus or minus 10 to 15 percent depending on tank age, ambient temperature, and regulator calibration drift. Critical Warnings The duty cycle is the hidden variable. Entering your flow rate without accounting for burn time produces an estimate that is often 3 to 4 times longer than reality. A regulator set to 1 SCFH running 15 minutes per hour consumes exactly 0.25 cu ft per active hour -- not 1. Every duration estimate that ignores this will be off by the same factor. Flow rate units must match. Regulator gauges in North America are commonly labeled in SCFH, but some imported units display LPM (liters per minute) or CFM (cubic feet per minute). Entering a CFM value as SCFH produces a result 60 times larger than actual. Verify your gauge's unit label before entering any number. Partial tanks produce pro-rated results. A 20 lb cylinder that is only half full contains the equivalent of a 10 lb fill. Always weigh the cylinder and subtract tare weight for mid-cycle calculations. CO2 enrichment without adequate light produces minimal crop benefit. Elevated CO2 increases photosynthesis rates only when light levels are also elevated. Using this DLI calculator alongside CO2 duration planning helps ensure your light and gas schedules are aligned for actual plant response. Minimum Standards For most indoor cannabis and vegetable crops, a target of 1,000 to 1,500 ppm CO2 is standard. A practical midpoint of 1,200 ppm is widely referenced across controlled environment agriculture guidelines. CO2 enrichment is only productive during the photoperiod. Running CO2 during dark hours in a sealed room produces no photosynthetic benefit and wastes supply. Set your daily use hours to match your light-on period. For greenhouse applications where natural CO2 exchange occurs through vents, enrichment is most effective when ventilation is minimized. The greenhouse CO2 calculator accounts for room volume and exchange rate to help size supplementation correctly for non-sealed environments. Competitor Trap: Most CO2 duration calculators on the web use a simplified formula: Gas Volume / Flow Rate. That approach assumes the regulator runs continuously at full flow, 24 hours a day, which is almost never how grow room CO2 systems operate. The result is a duration estimate that overstates actual tank life by a factor proportional to your duty cycle. A timer set to 15 minutes on, 45 minutes off means the true consumption rate is one quarter of the regulator's stated flow. Calculators that omit burn time and daily hours are not calculating your situation -- they are calculating a theoretical maximum that no real installation matches. Tools that also ignore the CO2 burner heat load produced by propane or natural gas CO2 generators miss an additional variable; those systems interact with the CO2 burner heat load in ways that require separate AC or ventilation sizing.

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## Provenance

- Model ID: `tyg-692`
- Model version: `1.0.0`
- Reviewed by: Umer Hayiat
- Page modified: 2026-08-20T09:58:54
- Runtime SHA-256: `de0b6958516a74a8d5421d2589515cfd2cf5a984293ec3677b80f06d16db1947`

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