PumpendiumThe spec reference for home pumps

Calculator

Sump pump sizing calculator (total dynamic head)

Measure from the bottom of the pit to where the pipe leaves the house, add the pipe run and fittings, and see your total dynamic head and the pumps that can reach it.

Pit bottom to the highest point of the discharge pipe
Pipe length from the top of the riser to the outlet
Count each 90; two 45s count as about one
40 GPM = 2,400 GPH, a common target for a 1/3 HP pump

How the math works

Pumpendium mathTotal dynamic head (TDH) = vertical lift + friction loss. Friction uses the Hazen-Williams equation for PVC (C = 150): loss in feet = 10.44 × equivalent length × (GPM ÷ 150)1.852 ÷ inside diameter4.8655. Equivalent length = vertical pipe + horizontal run + each fitting's equivalent length (for 1-1/2 in pipe: 4 ft per 90-degree elbow, 7.5 ft for a silent check valve, 13 ft for a swing check valve).
LimitsA pump's maximum head is where its flow drops to zero, so a pump with only a little head to spare moves very little water at your height. Use the maker's flow curve to read the flow at your TDH. Very long runs, many fittings or an undersized pipe raise friction quickly.

Questions

What is total dynamic head?
It is the total height the pump has to push against: the vertical lift plus the extra resistance of the pipe, elbows and check valve at your flow rate.
Why does pipe size matter so much?
Friction falls steeply as the pipe gets wider. At 40 GPM, 1-1/4 in pipe loses more than twice as much head per foot as 1-1/2 in pipe.
How much head should I have to spare?
Pick a pump whose curve still delivers the flow you need at your TDH. As a rough screen, a maximum head well above your TDH (we flag 25% or more) leaves room for useful flow.