Sump Pump Capacity Calculator

Inputs

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Basement, footing-drain or exterior area that can feed the sump. Use the area your waterproofing/drainage path actually collects.
ft²
Area-based water entry rate expressed like rainfall depth over the contributing area. Use measured inflow when you have it.
in/h
Fraction of the area water-entry estimate assumed to reach the sump.
Measured seepage, drain-tile flow, condensate or other direct inflow added to the area-based estimate.
gpm
Extra inflow allowance for storm variation, sediment, partial blockage, pump wear and uncertainty.
%
Pump flow at the installed total dynamic head, from the manufacturer pump curve. Do not use zero-head rating.
gpm
Inside sump basin diameter used for drawdown volume.
in
Water depth when the float or controller starts the pump.
in
Water depth when the pump stops. Must be below pump-on depth.
in
Alarm or critical water depth above the pump-on setting.
in
Desired time to pump the on/off drawdown volume while design inflow continues.
min
User-entered cycling target for the pump and switch. Manufacturer data controls final limits.
/h

Results

Default result
Edit inputs
Design inflow(Qd)
19.19gpm
Pass

Area-based inflow: 29.50 L/min. Raw inflow before allowance: 48.42 L/min.

Also computed

Required pump capacity @ head(Qreq)Pass28.98gpm

Capacity needed at the installed total dynamic head to keep up with design inflow and pump down the basin drawdown volume in the target time.

Selected pump utilization(U)Pass72.45%

Basin drawdown volume(Vcyc)Pass19.58gal

High-water reserve volume above pump-on depth: 59.31 L.

Net pump-down flow(Qnet)Pass20.81gpm

Selected pump capacity at head minus design inflow. This must stay positive for the pump to lower the basin.

Pump run time(trun)Pass0.941min

Time to pump from pump-on depth down to pump-off depth while design inflow continues.

Fill time between cycles(tfill)1.021min

Time for design inflow to refill the basin from pump-off depth to pump-on depth.

Sump pump preview: required pump capacity 110 L per minute, selected pump 72 percent usedSump pump previewInflow, basin drawdown volume, pump-down time and cycle ratedesign inflow73 L/minrequired pump @ head110 L/minPump72%StartsScreen only. Final pump selection needs the pump curve at total dynamic head, check valve, discharge pipe, power, alarm and backup details.
Method notes 4 notes
  • Area inflow uses Q = C*i*A, then adds measured/direct inflow and applies the entered safety factor.
  • Required pump capacity is evaluated at the installed total dynamic head, not at zero-head catalog rating.
  • Cycle volume is the cylindrical basin volume between pump-on and pump-off depths; the high-water reserve is the volume between pump-on and alarm depth.
  • Final sump design still needs the pump curve, discharge pipe and check valve losses, solids handling, basin geometry, switch limits, power, alarm, backup pump, local plumbing/electrical requirements and waterproofing review.

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