Sump Pump Size Calculator
Estimate sump-pit active volume, fill time, required pump flow, capacity margin, cycles per hour and daily water removal.
Default project preview
12 gal/min
Active pit volume
8.8 gal
Fill time
1.1 min
Pump capacity margin
+13 gal/min
Estimated cycles
37 per hour
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Sump pit diameter
Enter this project assumption in in. The current imperial default is 18 in.
Pump-on to pump-off depth
Enter this project assumption in in. The current imperial default is 8 in.
Estimated inflow
Enter this project assumption in gal/min. The current imperial default is 8 gal/min.
Flow reserve
Enter this project assumption in %. The current imperial default is 50 %. Minimum: 0. Maximum: 100.
Pump capacity at design head
Enter this project assumption in gal/min. The current imperial default is 25 gal/min.
Vertical discharge lift
Enter this project assumption in ft. The current imperial default is 10 ft.
Pipe and fitting head loss
Enter this project assumption in ft. The current imperial default is 5 ft. Minimum: 0.
Pump price
Enter this project assumption in a unitless value. The current imperial default is 180. Minimum: 0.
How to read the outputs
Active pit volume
switching volume. Default preview: 8.8 gal.
Fill time
at entered inflow. Default preview: 1.1 min.
Pump capacity margin
above reserved requirement. Default preview: +13 gal/min.
Estimated cycles
steady-inflow model. Default preview: 37 per hour.
Discharge head
lift plus entered losses. Default preview: 15 ft.
Daily water volume
continuous inflow equivalent. Default preview: 11,520 gal.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Active pit volume is a cylinder. Required flow = inflow × reserve factor. Cycling combines pit fill time with pump-down time based on net removal flow.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 29, 2026
Use this calculator to compare required sump-pump flow with lift and reserve assumptions. Pump selection must ultimately use the manufacturer performance curve at the actual total dynamic head.
Calculation steps
- 1Estimate inflow under the design event.
- 2Add a reserve for uncertainty and cycling.
- 3Calculate vertical lift and approximate friction loss.
- 4Choose a pump whose curve exceeds the target at total head.
Worked numerical example
A basin receiving 20 gallons per minute with a 50% reserve creates a target of 30 gpm. A pump rated 30 gpm at zero head may deliver much less at the installed lift and pipe resistance.
Purchasing and rounding
Do not choose from horsepower or shutoff head alone. The pump curve, discharge size, check valve, backup power and alarm are separate selection factors.
Interpret the result
The flow target is a planning requirement. Frequent short cycles may indicate a small basin or switch range even when pump flow is adequate.
Page-specific assumptions
- Inflow estimate is representative.
- One operating pump unless redundancy is modeled.
- Discharge remains open.
- Head losses are approximated separately.
Common mistakes
- Reading the zero-head rating.
- Ignoring check-valve and fitting losses.
- Selecting a pump without backup planning.
- Using basin volume as inflow rate.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Sump Pump Size Calculator questions
Why use pump capacity at design head?+
Published zero-head flow is higher than the flow available after vertical lift and pipe losses.
What happens if pump capacity is below inflow?+
The water level continues rising, so the pump is undersized for the entered condition.
Should a backup pump be installed?+
Backup pumping, battery power and alarms are often considered where flooding would cause significant damage.