Well Pump Total Dynamic Head & HP Guide
Add up the total dynamic head your well pump must work against — the depth it lifts water from, the pressure it maintains, and pipe friction — then read a rough horsepower tier. The HP tier is a planning guide, not a spec.
Calculator
Total dynamic head is about 241.2 ft (pumping level 180 + pressure head 46.2 + friction 15), which sits in the 3/4–1 HP class planning tier. HP tiers are a rough guide, not a spec — a pump installer sizes for your GPM at this head from the pump curve.
Choosing a submersible pump starts with total dynamic head (TDH), the total resistance the pump pushes against. It is not one number you look up — it is the sum of the lift from the pumping water level, the pressure you want to hold, and friction in the pipe. Get TDH right and the horsepower and pump model follow from the manufacturer’s performance curve; get it wrong and the pump is either starved or oversized.
Formula
Total dynamic head (TDH) is the sum of three heads the pump works against, all expressed in feet:
TDH = pumping water level + (psi × 2.31) + friction loss
Pressure converts to head at 2.31 feet per psi. The pumping water level is the depth to water while the pump is running (the drawn-down level), which sits below the static level. Friction loss is the head given up to pipe and fittings along the drop pipe and the run to the tank.
Worked example
A pump drawing from a pumping level of 180 ft, holding 20 psi of system pressure, with 15 ft of friction loss:
pressure head = 20 × 2.31 = 46.2 ftTDH = 180 + 46.2 + 15 = 241.2 ft
A total dynamic head of about 241 ft lands in the mid horsepower planning tier. The exact horsepower still depends on the GPM you need at that head — the installer reads it off the pump’s performance curve, where flow and head trade against each other.
Reading a pump curve, not a horsepower label
Total dynamic head is the single most important number for choosing a submersible pump, because a pump’s output is not a fixed GPM — it is a curve. The same pump delivers more flow at low head and less at high head. Sizing means finding a pump whose curve passes through your target flow (from the required GPM tool) at your calculated head.
The horsepower tier shown here is deliberately rough. Two pumps of the same horsepower can have very different curves, and a well-matched smaller pump often beats an oversized one: an oversized pump short-cycles, wastes energy, and can even out-pump the well and draw it down. So use the tier to get in the right neighborhood, then let a professional pick the exact model from the curve at your flow and head.
Two practical cautions. First, use the pumping level, not the static level — a well can sit at 120 ft static but draw down to 180 ft while pumping, and sizing to the static level under-sizes the pump. Second, friction loss grows quickly with flow and with small-diameter pipe over a long run; if the run to the house is long, larger drop pipe or supply pipe can matter as much as horsepower.
Reference table
Informational planning tiers by total dynamic head — the final choice comes from the pump curve at your required GPM, made by a pump installer.
| Total dynamic head | Rough HP tier |
|---|---|
| Up to ~150 ft | 1/2 HP class |
| ~150 to ~300 ft | 3/4 to 1 HP class |
| More than ~300 ft | 1.5 HP and up class |
Frequently asked questions
What is total dynamic head on a well pump?
Total dynamic head is the total resistance a pump works against, in feet: the depth it lifts water from while running, plus the pressure it maintains (converted at 2.31 ft per psi), plus friction loss in the pipe. It is the head value you match against a pump’s performance curve to pick the right model.
How do I convert psi to feet of head?
Multiply psi by 2.31. So 20 psi is about 46.2 ft of head, and 50 psi is about 115.5 ft. This lets you add the pressure you want at the tank to the lift and friction on the same scale.
Should I use the static or the pumping water level?
Use the pumping (drawn-down) level, the depth to water while the pump runs. It sits below the static level because pumping lowers the water in the well. Sizing to the static level under-estimates the head and under-sizes the pump.
Is the horsepower tier a specification?
No. It only puts you in the right range. Actual horsepower depends on the GPM you need at your head, and two same-horsepower pumps can have very different curves. A pump installer sizes the exact model from the curve; an oversized pump short-cycles and can out-pump the well.