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Pumps & Rotating Equipment

What Is Pump Head?

Pump head is energy per unit weight of fluid, expressed as an equivalent height of liquid column. Learn why it matters for pump selection and how it relates to pressure.

TypeEngineering guide — concept explainer

Definition

Pump head is the energy imparted to a fluid by a pump, expressed as the equivalent height of a liquid column that the pump could sustain. It has units of length (typically metres or feet) and is independent of the fluid's density. This makes head useful for comparing pump performance across different fluids using a single pump curve.

Why it matters

Engineers use head rather than pressure when selecting pumps because a pump curve plotted in head applies to any liquid — water, brine, or oil — without re-drawing. The actual pressure difference depends on the fluid density and gravity, but the head stays the same for a given flow rate on the same pump. Misunderstanding this relationship leads to incorrect pump sizing, especially when switching between metric and imperial units.

Formula

Pressure from head
ΔP = ρ × g × h
Head from pressure
h = ΔP / (ρ × g)

Units involved

  • •h — head in metres (m) or feet (ft)
  • •ΔP — pressure difference in pascals (Pa) or psi
  • •ρ — fluid density in kg/m³ or lb/ft³
  • •g — gravitational acceleration, 9.80665 m/s²

Concept diagram

reservoirpumphdischargeΔP = ρgh

Worked example

A pump must deliver water to a tank 10 metres above the pump centreline. What is the corresponding pressure at the pump discharge, assuming water density of 998 kg/m³?

  1. 01h = 10 m
  2. 02ρ = 998 kg/m³
  3. 03g = 9.80665 m/s²
  4. 04ΔP = 998 × 9.80665 × 10
  5. 05ΔP = 97,890 Pa ≈ 97.9 kPa
Result

10 m of water head ≈ 97.9 kPa (≈ 0.979 bar)

Common mistakes

  • •Confusing head with pressure — head is density-independent; pressure is not.
  • •Forgetting to convert units — mixing metres and feet, or kg/m³ and lb/ft³, without adjusting the formula.
  • •Using pump head for NPSH calculations without separating static head, velocity head, and friction losses.
  • •Assuming head equals elevation difference — pump head also includes friction losses, velocity head changes, and pressure head at suction/discharge.

When to use the calculator

Use the Head to Pressure calculator when you know the head and need the corresponding pressure (or vice versa). Use the Pump Power calculator when you also know the flow rate and pump efficiency and need the hydraulic power.

Head to Pressure Calculator →Pump Hydraulic Power Calculator →

FAQ

What is the difference between pump head and discharge pressure?
Pump head is energy per unit weight of fluid, expressed as an equivalent height. Discharge pressure is force per unit area. They are related by ΔP = ρgh — the same head produces different pressures for different fluid densities.
Why do pump curves use head instead of pressure?
A pump curve plotted in head is valid for any liquid of any density (assuming similar viscosity). If the curve used pressure, you would need a separate curve for each fluid density.
Can I convert pump head directly to psi?
Yes, but you need the fluid density. For water at standard conditions: 1 m of head ≈ 9.79 kPa ≈ 1.42 psi. For other fluids, use ΔP = ρgh with the correct density.
Does pump head account for friction losses?
Total dynamic head (TDH) includes friction losses, but the basic head concept shown here is static head only. System head curves that include friction are a separate topic.