---
title: "Sump Pump Calculator: Find Your Basin Cycle Time and Stop Motor-Burning Short Cycles"
canonical: "https://theyieldgrid.com/sump-pump-calculator/"
model_id: "tyg-796"
model_version: "1.0.0"
last_reviewed: "2026-08-20T10:00:42"
reviewed_by: "Umer Hayiat"
---

# Sump Pump Calculator: Find Your Basin Cycle Time and Stop Motor-Burning Short Cycles

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

## What this calculator does

Home - Free Gardening Calculators & Tools - Sump Pump Calculator: Find Your Basin Cycle Time and Stop Motor-Burning Short Cycles Calculate your pump cycle time and catch motor-damaging short cycles before they destroy your pump.

## Inputs

| Input | ID | Type | Unit | Range or choices | Required |
|---|---|---|---|---|---|
| Water Inflow Rate | `sumpbasin_inflow` | number |  | 0.1 to 200 | No |
| Pump Output at Head Height | `sumpbasin_pumpout` | number |  | 0.1 to 500 | No |
| Basin Diameter | `sumpbasin_diameter` | number |  | 6 to 96 | No |
| Float Switch On/Off Range | `sumpbasin_floatrange` | number | inches | 0.5 to 48 | No |

## Outputs

| Output ID | Default state |
|---|---|
| `sumpbasin_inflow_err` |  |
| `sumpbasin_pumpout_err` |  |
| `sumpbasin_diameter_err` |  |
| `sumpbasin_floatrange_err` |  |
| `sumpbasin_results` | Pump Cycle Time — minutes per cycle Cycle Safety Gauge DANGER 3 min Gallons per Inch — gal / inch Operating Volume — gallons Net Pump Rate — GPM (out − in) Cycles per Hour — starts / hr System Check Reference: Basin Size vs. Cycle Time at Your Conditions Basin Ø (in) Gal/inch Op. Volume (gal) Cycle Time (min) Rating How This Calculator Works Step 1 — Gallons per Inch of Basin Gallons/inch = π × (Diameter ÷ 2)² ÷ 231 231 cubic inches = 1 US gallon. This gives us the l |
| `sumpbasin_out_primary` | — |
| `sumpbasin_out_gpi` | — |
| `sumpbasin_out_vol` | — |
| `sumpbasin_out_net` | — |
| `sumpbasin_out_cph` | — |
| `sumpbasin_warn_box` | System Check |

## Formula and method

A visual breakdown of how basin diameter and float range determine the total gallons per cycle. Show the calculation steps Step 1: Gallons per Inch of Basin The basin is treated as a perfect cylinder. The cross-sectional area in square inches is computed using the standard circle area formula (pi times radius squared). That area is then divided by 231, which is the number of cubic inches in one US gallon. The result is how many gallons of water are added or removed for each vertical inch of level change inside the pit. Formula: Gallons per Inch = pi x (Diameter / 2)^2 / 231 Units: diameter in inches; result in gallons per inch. No unit conversion is required for the intermediate step. Step 2: Operating Volume Operating volume is the total gallons the pump must remove each cycle. It is the product of gallons per inch and the float switch activation range in inches. This represents the column of water between the pump-on and pump-off water levels. Formula: Operating Volume (gallons) = Gallons per Inch x Float Switch Range (inches) Step 3: Net Pump Rate While the pump runs, water is simultaneously entering the pit. The effective emptying rate is pump output minus inflow, both in GPM. If inflow equals or exceeds pump output, the net rate is zero or negative, meaning the pump cannot lower the water level at all. Formula: Net Rate (GPM) = Pump Output (GPM) - Inflow (GPM) Step 4: Cycle Time Cycle time is how long the pump runs from turn-on to turn-off. It equals the operating volume divided by the net pumping rate. The result is in minutes if GPM and gallons are used consistently. No unit conversion is needed. Formula: Cycle Time (minutes) = Operating Volume (gallons) / Net Rate (GPM) Rounding: Results are displayed to three decimal places in intermediate steps and two decimal places in the final output. Gallons per inch is shown to three decimal places due to its impact on downstream precision. Step 5: Starts per Hour Starts per hour is derived by dividing 60 minutes by the cycle time. This assumes the fill time between cycles is negligible compared to cycle time, which is a reasonable approximation at high inflow rates but becomes less accurate at very low inflow rates where refill time is long. Formula: Starts per Hour = 60 / Cycle Time (minutes) Assumptions and Limits The basin is a perfect vertical cylinder. Irregular or rectangular pit shapes require a different volume calculation. Inflow rate is constant throughout the pump cycle. In reality, storm runoff inflow fluctuates; this calculator uses a steady-state approximation. Pump output is constant at the entered GPM. In practice, pump output can vary slightly with fluctuating head pressure as water level changes. Float switch range is measured as vertical inches only. Tethered float switches have variable effective range depending on cord length and mounting position; the calculation assumes a clean, repeatable on/off activation point. Pipe friction losses inside the discharge line are not accounted for in the inflow or output fields. The user is responsible for entering a head-corrected pump GPM that already reflects discharge pipe conditions. The refill time between cycles (pump off to pump on) is not included in the starts-per-hour estimate. At very low inflow rates, actual starts per hour will be lower than calculated because the pit takes longer to refill. Motor startup amperage draw is referenced qualitatively as a warning threshold trigger (cycle time below 1 minute), not computed numerically. Actual amperage depends on motor type, winding configuration, and supply voltage.

## Verified worked examples

### Scenario 1: Oversized 1 HP Pump in a Standard 18-Inch Basin

Water inflow rate: 10 GPM (typical during heavy rain) Pump output at head height: 45 GPM (1 HP pump at 10 ft head) Basin diameter: 18 inches Float switch range: 6 inches Result: Gallons per inch = 1.102; Operating volume = 6.61 gallons; Net pump rate = 35 GPM; Cycle time = 0.189 minutes (approximately 11 seconds); Starts per hour = 318. At 318 motor starts per hour, the stator windings experience locked rotor amperage surges continuously. This is the textbook "stator meltdown" scenario: an oversized, seemingly high-performance pump destroying itself in a pit that cannot supply enough water volume to keep the motor running long enough to cool. The fix is not a better pump; it is a correctly sized basin or a lower-output pump matched to the inflow rate.

### Scenario 2: Moderate Mismatch in a 24-Inch Basin

Water inflow rate: 15 GPM Pump output at head height: 25 GPM Basin diameter: 24 inches Float switch range: 10 inches Result: Gallons per inch = 1.958; Operating volume = 19.58 gallons; Net pump rate = 10 GPM; Cycle time = 1.958 minutes; Starts per hour = 30.6. The cycle time clears the 1-minute danger threshold but falls short of the 3-minute safe minimum. At roughly 30 starts per hour, motor stress is elevated. The simplest correction here is widening the float switch range to 18 inches, which would push operating volume to 35.2 gallons and cycle time to 3.52 minutes with no hardware changes.

### Scenario 3: Properly Sized 30-Inch Basin

Water inflow rate: 10 GPM Pump output at head height: 22 GPM Basin diameter: 30 inches Float switch range: 14 inches Result: Gallons per inch = 3.060; Operating volume = 42.84 gallons; Net pump rate = 12 GPM; Cycle time = 3.570 minutes; Starts per hour = 16.8. The cycle time sits above the 3-minute safe threshold and starts per hour are within reasonable operating range for most residential motors. This combination works because the basin diameter is large enough to hold meaningful volume per inch, and the pump output is appropriately matched to the inflow rather than dramatically oversized.

## Assumptions

Water inflow rate: 10 GPM (typical during heavy rain) Pump output at head height: 45 GPM (1 HP pump at 10 ft head) Basin diameter: 18 inches Float switch range: 6 inches Result: Gallons per inch = 1.102; Operating volume = 6.61 gallons; Net pump rate = 35 GPM; Cycle time = 0.189 minutes (approximately 11 seconds); Starts per hour = 318. At 318 motor starts per hour, the stator windings experience locked rotor amperage surges continuously. This is the textbook "stator meltdown" scenario: an oversized, seemingly high-performance pump destroying itself in a pit that cannot supply enough water volume to keep the motor running long enough to cool. The fix is not a better pump; it is a correctly sized basin or a lower-output pump matched to the inflow rate. A visual breakdown of how basin diameter and float range determine the total gallons per cycle. Show the calculation steps Step 1: Gallons per Inch of Basin The basin is treated as a perfect cylinder. The cross-sectional area in square inches is computed using the standard circle area formula (pi times radius squared). That area is then divided by 231, which is the number of cubic inches in one US gallon. The result is how many gallons of water are added or removed for each vertical inch of level change inside the pit. Formula: Gallons per Inch = pi x (Diameter / 2)^2 / 231 Units: diameter in inches; result in gallons per inch. No unit conversion is required for the intermediate step. Step 2: Operating Volume Operating volume is the total gallons the pump must remove each cycle. It is the product of gallons per inch and the float switch activation range in inches. This represents the column of water between the pump-on and pump-off water levels. Formula: Operating Volume (gallons) = Gallons per Inch x Float Switch Range (inches) Step 3: Net Pump Rate While the pump runs, water is simultaneously entering the pit. The effective emptying rate is pump output minus inflow, both in GPM. If inflow equals or exceeds pump output, the net rate is zero or negative, meaning the pump cannot lower the water level at all. Formula: Net Rate (GPM) = Pump Output (GPM) - Inflow (GPM) Step 4: Cycle Time Cycle time is how long the pump runs from turn-on to turn-off. It equals the operating volume divided by the net pumping rate. The result is in minutes if GPM and gallons are used consistently. No unit conversion is needed. Formula: Cycle Time (minutes) = Operating Volume (gallons) / Net Rate (GPM) Rounding: Results are displayed to three decimal places in intermediate steps and two decimal places in the final output. Gallons per inch is shown to three decimal places due to its impact on downstream precision. Step 5: Starts per Hour Starts per hour is derived by dividing 60 minutes by the cycle time. This assumes the fill time between cycles is negligible compared to cycle time, which is a reasonable approximation at high inflow rates but becomes less accurate at very low inflow rates where refill time is long. Formula: Starts per Hour = 60 / Cycle Time (minutes) Assumptions and Limits The basin is a perfect vertical cylinder. Irregular or rectangular pit shapes require a different volume calculation. Inflow rate is constant throughout the pump cycle. In reality, storm runoff inflow fluctuates; this calculator uses a steady-state approximation. Pump output is constant at the entered GPM. In practice, pump output can vary slightly with fluctuating head pressure as water level changes. Float switch range is measured as vertical inches only. Tethered float switches have variable effective range depending on cord length and mounting position; the calculation assumes a clean, repeatable on/off activation point. Pipe friction losses inside the discharge line are not accounted for in the inflow or output fields. The user is responsible for entering a head-corrected pump GPM that already reflects discharge pipe conditions. The refill time between cycles (pump off to pump on) is not included in the starts-per-hour estimate. At very low inflow rates, actual starts per hour will be lower than calculated because the pit takes longer to refill. Motor startup amperage draw is referenced qualitatively as a warning threshold trigger (cycle time below 1 minute), not computed numerically. Actual amperage depends on motor type, winding configuration, and supply voltage. The basin is a perfect vertical cylinder. Irregular or rectangular pit shapes require a different volume calculation. Inflow rate is constant throughout the pump cycle. In reality, storm runoff inflow fluctuates; this calculator uses a steady-state approximation. Pump output is constant at the entered GPM. In practice, pump output can vary slightly with fluctuating head pressure as water level changes. Float switch range is measured as vertical inches only. Tethered float switches have variable effective range depending on cord length and mounting position; the calculation assumes a clean, repeatable on/off activation point. Pipe friction losses inside the discharge line are not accounted for in the inflow or output fields. The user is responsible for entering a head-corrected pump GPM that already reflects discharge pipe conditions. The refill time between cycles (pump off to pump on) is not included in the starts-per-hour estimate. At very low inflow rates, actual starts per hour will be lower than calculated because the pit takes longer to refill. Motor startup amperage draw is referenced qualitatively as a warning threshold trigger (cycle time below 1 minute), not computed numerically. Actual amperage depends on motor type, winding configuration, and supply voltage. Critical Warnings Sub-1-minute cycle time triggers motor burnout risk. At startup, electric motors draw locked rotor amperage, which is approximately three times the normal running current. A pump cycling every 11 seconds (as in Scenario 1 above) experiences hundreds of these high-current surges per hour. Heat cannot dissipate from the stator windings between starts. Insulation degrades, copper oxidizes, and the winding fails. This process can destroy a new motor within days or weeks, not years. Starts per hour above 10 exceeds most residential motor ratings. Many residential sump pump motors carry a manufacturer-rated maximum of 8 to 10 starts per hour. Operating above this threshold voids warranties on most major brands and accelerates bearing wear in addition to winding stress. The calculator flags this threshold separately from the cycle-time danger zone. Zero or negative net rate means the pump cannot control the water level. If entered pump output is equal to or less than inflow, no cycle time exists. The basin will fill continuously. This is not a marginal condition; it requires a larger pump, reduced inflow, or both. Sites with heavy surface water contributions may need upstream catch basin drainage to reduce the inflow GPM before pump sizing makes sense. Head pressure degrades pump output more than most labels suggest. A pump marketed as a 1/2 HP, 35 GPM unit delivers that figure at zero head. At 10 feet of vertical head with a typical discharge run, output may drop to 18 to 22 GPM. Entering the zero-head rating into this calculator will produce a falsely optimistic cycle time. Minimum Standards Target a minimum cycle time of 3 minutes to allow adequate motor cooling between starts. Keep starts per hour at or below 10 for residential pump motors unless the manufacturer's documentation specifies otherwise. Verify pump GPM from the manufacturer's published performance curve, not from product packaging or marketing materials. Float switch range should be maximized within the constraints of the basin depth and discharge pipe connection height to increase operating volume and extend cycle time. Competitor Trap Most sump pump sizing guides focus exclusively on whether the pump output is large enough to handle inflow, and stop there. That framing misses the core failure mechanism entirely. An oversized pump is often more dangerous than an undersized one in a typical residential basin. A pump that can outrun inflow by a factor of four empties a small pit in seconds, cycles hundreds of times per hour, and burns out in weeks, while a homeowner assumes it failed due to a defect. The correct question is not "is my pump big enough?" but "does my basin hold enough volume to keep my pump cycling at a safe rate?" This calculator addresses the second question, which the first question leaves completely unanswered. If you are also evaluating your property's total water collection and catchment volume from rain events , understanding how much water reaches your foundation helps inform a more accurate inflow estimate for this tool. Target a minimum cycle time of 3 minutes to allow adequate motor cooling between starts. Keep starts per hour at or below 10 for residential pump motors unless the manufacturer's documentation specifies otherwise. Verify pump GPM from the manufacturer's published performance curve, not from product packaging or marketing materials. Float switch range should be maximized within the constraints of the basin depth and discharge pipe connection height to increase operating volume and extend cycle time.

## Limitations and safety

The basin is a perfect vertical cylinder. Irregular or rectangular pit shapes require a different volume calculation. Inflow rate is constant throughout the pump cycle. In reality, storm runoff inflow fluctuates; this calculator uses a steady-state approximation. Pump output is constant at the entered GPM. In practice, pump output can vary slightly with fluctuating head pressure as water level changes. Float switch range is measured as vertical inches only. Tethered float switches have variable effective range depending on cord length and mounting position; the calculation assumes a clean, repeatable on/off activation point. Pipe friction losses inside the discharge line are not accounted for in the inflow or output fields. The user is responsible for entering a head-corrected pump GPM that already reflects discharge pipe conditions. The refill time between cycles (pump off to pump on) is not included in the starts-per-hour estimate. At very low inflow rates, actual starts per hour will be lower than calculated because the pit takes longer to refill. Motor startup amperage draw is referenced qualitatively as a warning threshold trigger (cycle time below 1 minute), not computed numerically. Actual amperage depends on motor type, winding configuration, and supply voltage. Critical Warnings Sub-1-minute cycle time triggers motor burnout risk. At startup, electric motors draw locked rotor amperage, which is approximately three times the normal running current. A pump cycling every 11 seconds (as in Scenario 1 above) experiences hundreds of these high-current surges per hour. Heat cannot dissipate from the stator windings between starts. Insulation degrades, copper oxidizes, and the winding fails. This process can destroy a new motor within days or weeks, not years. Starts per hour above 10 exceeds most residential motor ratings. Many residential sump pump motors carry a manufacturer-rated maximum of 8 to 10 starts per hour. Operating above this threshold voids warranties on most major brands and accelerates bearing wear in addition to winding stress. The calculator flags this threshold separately from the cycle-time danger zone. Zero or negative net rate means the pump cannot control the water level. If entered pump output is equal to or less than inflow, no cycle time exists. The basin will fill continuously. This is not a marginal condition; it requires a larger pump, reduced inflow, or both. Sites with heavy surface water contributions may need upstream catch basin drainage to reduce the inflow GPM before pump sizing makes sense. Head pressure degrades pump output more than most labels suggest. A pump marketed as a 1/2 HP, 35 GPM unit delivers that figure at zero head. At 10 feet of vertical head with a typical discharge run, output may drop to 18 to 22 GPM. Entering the zero-head rating into this calculator will produce a falsely optimistic cycle time. Minimum Standards Target a minimum cycle time of 3 minutes to allow adequate motor cooling between starts. Keep starts per hour at or below 10 for residential pump motors unless the manufacturer's documentation specifies otherwise. Verify pump GPM from the manufacturer's published performance curve, not from product packaging or marketing materials. Float switch range should be maximized within the constraints of the basin depth and discharge pipe connection height to increase operating volume and extend cycle time. Competitor Trap Most sump pump sizing guides focus exclusively on whether the pump output is large enough to handle inflow, and stop there. That framing misses the core failure mechanism entirely. An oversized pump is often more dangerous than an undersized one in a typical residential basin. A pump that can outrun inflow by a factor of four empties a small pit in seconds, cycles hundreds of times per hour, and burns out in weeks, while a homeowner assumes it failed due to a defect. The correct question is not "is my pump big enough?" but "does my basin hold enough volume to keep my pump cycling at a safe rate?" This calculator addresses the second question, which the first question leaves completely unanswered. If you are also evaluating your property's total water collection and catchment volume from rain events , understanding how much water reaches your foundation helps inform a more accurate inflow estimate for this tool.

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## Provenance

- Model ID: `tyg-796`
- Model version: `1.0.0`
- Reviewed by: Umer Hayiat
- Page modified: 2026-08-20T10:00:42
- Runtime SHA-256: `0cff1208a89963aafcbed108df97080b69724566c9454a441dc98de562dcc6fe`

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