Pump Head Calculator — Total Dynamic Head
A pump is selected against a curve, not a horsepower, and the number you take to that curve is total dynamic head — everything the pump has to overcome, expressed in feet. Four terms make it up: the vertical lift, the friction in the discharge pipe, any pressure the outlet has to deliver at, and the velocity of the water itself. This adds them and shows what share each takes.
Work out the head
Water level to discharge point, vertically.
Including fitting equivalents.
Zero for an open discharge such as a sump. A booster feeding a system needs the real figure.
Total dynamic head
Static lift dominates at 83% of the total, so pipe size makes little difference here.
Friction head
2.08 ft
Discharge velocity
4.73 ft/s
See the breakdown
Planning estimate. Net positive suction head, cavitation margin and pump-curve efficiency are not modelled — a surface pump can only lift about 25 ft on the suction side at sea level whatever this says. A licensed plumber and the pump manufacturer's curve have final say.
The formula, explained in plain English
Four terms, all converted to feet so they can be added, then matched against a pump curve.
Everything in feet, not psi
Pump curves are published in feet of head because feet are independent of fluid density. Convert every term to feet first, add them, and only convert to psi at the end if you need to.
Static lift is not negotiable
It is a measured dimension. Friction you can design down by upsizing the discharge; pressure head depends on what you are feeding; lift is whatever the building is.
Velocity head is honest but tiny
At 4.73 ft/s it is 0.35 feet — 2.4% of the default total. It belongs in the equation and it will not change your pump. Including it and saying it is small beats quietly dropping it.
Oversizing has a cost
A pump running far from its best efficiency point short-cycles, wears its seals and can cavitate. Match the curve near the duty point rather than buying the biggest unit that fits.
Worked examples
A basement sump, a long run where friction takes over, and a booster where pressure head dominates.
Basement sump — 30 gpm, 12 ft lift
40 ft of 1-1/2 inch PVC, open discharge. The calculator's defaults.
friction = 0.90 psi × 2.309 = 2.08 ft (14%)
pressure = 0 ft · velocity 4.73 ft/s → 0.35 ft (2.4%)
TDH = 14.43 ft = 6.25 psi
Result: find a pump delivering 30 gpm at 14.4 feet. Static lift is five sixths of the job — no realistic pipe change moves this number much.
Long discharge to a ditch — friction takes over
Same 30 gpm and 12 ft lift, but 300 ft of 1-1/2 inch PVC to reach the outfall.
TDH = 12 + 15.63 + 0 + 0.35 = 27.97 ft
friction is now 56% of the total
upsize to 2": friction drops to 4.63 ft → TDH = 16.76 ft
Result: the same pit and the same lift need nearly twice the head, purely because of the run. Here the discharge pipe size is the whole design decision — one size up removes 11.2 feet of head.
Booster pump — pressure head dominates
20 gpm, 30 ft of lift, 100 ft of 1-1/4 inch copper, and 40 psi required at the outlet.
static = 30 ft · friction 9.04 ft · velocity head 0.41 ft
TDH = 131.80 ft
pressure head alone is 70% of it
Result: on a booster the required discharge pressure swamps everything else. Forty psi is worth ninety-two feet of head — three times the actual lift — which is why booster duty points look so different from sump duty points.
Discharge size against head — 30 gpm, 40 ft, 12 ft lift
Schedule 40 PVC, computed from the same code the calculator runs. Watch how quickly the friction term collapses, and how little the total moves once it has.
| Discharge size | Velocity | Friction head | Velocity head | TDH |
|---|---|---|---|---|
| 1" | 11.14 ft/s | 16.79 ft | 1.927 ft | 30.71 ft |
| 1-1/4" | 6.44 ft/s | 4.41 ft | 0.644 ft | 17.06 ft |
| 1-1/2" | 4.73 ft/s | 2.08 ft | 0.347 ft | 14.43 ft |
| 2" | 2.87 ft/s | 0.62 ft | 0.128 ft | 12.74 ft |
| 2-1/2" | 2.01 ft/s | 0.26 ft | 0.063 ft | 12.32 ft |
| 3" | 1.30 ft/s | 0.09 ft | 0.026 ft | 12.12 ft |
| 4" | 0.76 ft/s | 0.02 ft | 0.009 ft | 12.03 ft |
Static lift against total — 30 gpm, 1-1/2 inch, 40 ft
The share column is the useful one: past about 10 feet of lift, the pipe stops mattering.
| Static lift | Friction head | TDH | Static share |
|---|---|---|---|
| 5 ft | 2.08 ft | 7.43 ft | 67% |
| 10 ft | 2.08 ft | 12.43 ft | 80% |
| 12 ft | 2.08 ft | 14.43 ft | 83% |
| 15 ft | 2.08 ft | 17.43 ft | 86% |
| 20 ft | 2.08 ft | 22.43 ft | 89% |
| 30 ft | 2.08 ft | 32.43 ft | 93% |
Sources & standards: total dynamic head as defined in standard pump engineering practice; friction from the Hazen-Williams equation as used in IPC Appendix E and ASPE guidance; velocity head from V² ÷ 2g with g = 32.174 ft/s²; pipe dimensions from ASTM D1785 and B88, with every bore computed from outside diameter and wall thickness. Net positive suction head and cavitation are not modelled — match the manufacturer's curve.
Frequently asked questions
Common questions about total dynamic head, static lift, and matching a pump curve.
What head does my pump need?
For a typical sump — 30 gpm up a 12-foot lift through 40 feet of 1-1/2 inch PVC — the answer is 14.43 feet of total dynamic head. Those are the defaults above. Pick a pump whose curve delivers 30 gpm at 14.4 feet or better; the curve, not the horsepower, is what you match against.
What is total dynamic head?
Everything the pump has to overcome, added up in feet. Static lift is the vertical rise. Friction head is what the pipe and fittings cost. Pressure head is any pressure the discharge has to be delivered at. Velocity head is the energy in the moving water itself. In the defaults those are 12, 2.08, 0 and 0.35 feet.
Can I ignore velocity head?
Usually, and it is honest to say so. In the defaults velocity head is 0.35 feet — 2.4% of the total. It is real, it belongs in the equation, and it almost never changes which pump you buy. Static lift is 83% of that same total. Spend your attention there.
Why does the discharge pipe size matter?
Because friction head is the term you can actually design away. Going from 1-1/2 inch to 2 inch PVC on the defaults cuts the friction from 2.08 feet to about 0.6 — a small absolute saving here, but on a long run or a higher flow it dominates. When the calculator says friction is the bigger share, upsizing the discharge is the cheapest fix available.
How do I convert head in feet to psi?
Divide by 2.309, or multiply by 0.4331. The default 14.43 feet of head is 6.25 psi. Pump curves are published in feet, plumbing pressure in psi, and you will convert between them constantly — the breakdown panel shows both.
Should I add a safety margin to the head?
A modest one, and put it in the right place. Adding 10% to friction head is reasonable because fittings get missed and pipe roughens with age. Do not pad the static lift — it is a measured dimension, not an estimate. And avoid oversizing badly: a pump running far left of its best efficiency point cycles more, wears faster and can cavitate.
Does this cover suction lift for a well pump?
Only as part of the static term. A surface pump lifting water from below itself is also limited by net positive suction head — practically about 25 feet at sea level and less with altitude or warm water, because atmospheric pressure is doing the lifting. Beyond that you need a submersible or a jet pump, and this calculator will not warn you about it.
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