Size a well pump correctly: total head including the pressure-tank cut-out conversion (the term DIYers forget), a submersible-vs-jet recommendation by depth, an HP range, and a well-yield warning to prevent pump burnout.
US + metric
Formula shown
Shareable results
Well Pump Sizing
ft
ft
gpm
baths
gpm
psi
psi
ft
ft
Total dynamic head238 ft(recommend 1.5–2 hp)
Recommended pump type: Deep-well jet or submersible (submersible preferred)
The pressure-tank cut-out converts to head at 2.31 ft per psi — usually the largest single term. Head is a planning estimate; verify against the pump curve and your well test. The yield warning guards against pump-off (running the well dry), the top cause of submersible burnout.
For preliminary sizing and educational use. Verify against the pump performance curve, well test data, and local codes; well and pump work is often best done by a licensed contractor.
Sizing a well pump is mostly about head, and the biggest piece of that head is usually the pressure tank — not the depth of the well. The pump must lift water from the pumping level to the surface, raise it to the highest fixture, overcome pipe friction, and pressurise the tank to its cut-out setting. That last part trips up most do-it-yourselfers, because the tank pressure has to be converted from psi to feet of head.
The mistake almost everyone makes: forgetting the pressure conversion
A pressure tank set to cut out at 60 psi does not add 60 feet of head — it adds 60 × 2.31 = 139 feet. One psi equals about 2.31 feet of water column, so a 40/60 tank demands well over a hundred feet of head all by itself. Leave that term out and you will badly undersize the pump: in the worked example below, ignoring it cuts the head from about 238 feet to 99 feet and the pump from roughly 1.5 hp to well under 1 hp.
Worked example
A well with a 40 ft static level and 20 ft of drawdown has a 60 ft pumping level. Serving a 3-bathroom home (about 12 gpm) with a 40/60 tank, 100 ft of horizontal run, a 25 ft rise to the top floor, and 1-inch poly pipe:
Pumping level: 60 ft; rise to fixture: 25 ft
Pressure head: 60 psi × 2.31 = 139 ft
Friction: about 14 ft
Total dynamic head ≈ 238 ft → roughly a 1.5 hp submersible
Do not out-pump the well
The most damaging mistake is fitting a pump that draws more than the well can supply. If peak demand exceeds the well’s sustainable yield, the pump pulls the water level down to the intake, loses prime, and runs dry — and running dry destroys a submersible in short order. This calculator warns when your demand exceeds the yield. The fix is not a bigger pump: reduce the flow, add storage or a larger pressure tank, or use a pump and controller matched to a low-yield well. A submersible is the right choice for most wells with a pumping level past about 25 feet; shallow-well jet pumps are limited to shallow suction lifts, and deep-well jets to roughly 110 feet.
Variables
Symbol
Meaning
US unit
SI unit
h_pump
Pumping water level = static level + drawdown
ft
m
P_cut-out
Pressure-tank cut-out setting (u00d72.31 u2192 ft of head)
