SumpPumpSize Tip

Total dynamic head calculator for sump pumps

A pump curve shows how much water the pump moves at each head, so you need the head first. Total dynamic head is the vertical lift from the water in the pit to the highest point of the pipe, plus friction losses. SumpPumpSize adds the pipe length and the equivalent length of each elbow and the check valve, then uses the Hazen-Williams formula for PVC to work out the friction at your flow.

Sump pump sizing

1. Inflow test: let the pit fill with the pump off and time how fast the water rises.

2. Discharge line: from the pump to where the water leaves the pipe.

    Saved you some time? Leave a tip, entirely optional.

    For a short discharge line the lift dominates; on long horizontal runs or small pipe, friction can add several feet.

    How the sump pump size calculator works

    Inflow comes from a fill test: with the pump off, the water rises a measured height in a measured time. A round pit holds π × (diameter ÷ 2)² ÷ 231 gallons per inch, so the inflow in gallons per minute is gallons per inch × inches ÷ minutes. SumpPumpSize adds your safety margin to get the design flow. The head is the vertical lift from the water level in the pit to the highest point of the discharge line, plus friction: the pipe length plus the equivalent length of each 90° elbow and the check valve, times the Hazen-Williams friction loss for schedule 40 PVC (C = 150) at the design flow. Water horsepower is GPM × head ÷ 3,960, and the motor estimate assumes about 30% wire-to-water efficiency for a small submersible pump.

    Gallons per inch of sump pit

    Pit diameterGallons per inchGallons in 10 in
    14 in0.676.7
    16 in0.878.7
    18 in1.111
    20 in1.3613.6
    22 in1.6516.5
    24 in1.9619.6
    30 in3.0630.6
    36 in4.4144.1

    Head at 10 ft of lift, 20 ft of 1½ in pipe, 3 elbows and a check valve

    InflowDesign flow (+50%)Total headSuggested motor
    5 GPM450 GPH10.2 ft1/4 HP
    10 GPM900 GPH10.8 ft1/4 HP
    15 GPM1,350 GPH11.6 ft1/4 HP
    20 GPM1,800 GPH12.8 ft1/3 HP
    30 GPM2,700 GPH15.9 ft3/4 HP
    40 GPM3,600 GPH20.1 ft1½ HP

    Pump curves differ between brands and models, so always check the flow at your head on the maker's curve. Discharge must go where local rules allow, away from the foundation and not into a sanitary sewer. Results are estimates for planning.

    Frequently asked questions

    How do I calculate total dynamic head?

    TDH = vertical lift + friction loss. Friction = pipe length plus fitting equivalents × friction per foot at your flow and pipe size.

    Does horizontal pipe count as head?

    Not as lift, but it adds friction. A rough rule is 1 ft of head per 10 ft of horizontal pipe; this calculator works it out from the flow instead.

    How much head does a check valve add?

    It is equivalent to roughly 9–13 ft of pipe, depending on size, which at normal sump flows is a few tenths of a foot to a foot of head.

    Is SumpPumpSize free?

    Yes, with no sign-up or ads.

    Are my numbers saved?

    Yes, in this browser only.

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