Pump head is one of the two essential parameters — alongside flow rate — that define a pump's duty point. Calculating it correctly is the difference between a system that runs efficiently and one that under-performs, cavitates, or wastes energy. This guide explains the components of total dynamic head and how to calculate them for industrial and marine pump applications.
What is pump head?
Pump head is the height to which a pump can raise a column of liquid, expressed in metres (m) or feet (ft). It is a measure of the energy added to the fluid by the pump, independent of fluid density. The same pump produces the same head whether pumping water, diesel, or seawater — but a different pressure, because pressure depends on fluid density.
The relationship between head and pressure is:
Pressure (bar) = Head (m) × Density (kg/L) ÷ 10.2
For water at 20 °C, 10 metres of head equals approximately 1 bar.
The four components of total dynamic head
Total dynamic head (TDH) is the sum of four components:
- Static suction head (or lift) — the vertical distance from the fluid surface to the pump centreline. Positive if the fluid is above the pump (flooded suction), negative if below.
- Static discharge head — the vertical distance from the pump centreline to the highest point of discharge or the surface of the destination tank.
- Friction losses — energy lost as the fluid flows through pipes, fittings, valves, and equipment. Calculated using pipe friction tables or the Darcy-Weisbach equation.
- Pressure head — any pressurised tank or vessel at the suction or discharge, converted to equivalent metres of head.
Step-by-step calculation example
Consider a typical industrial water transfer:
- Pump takes water from an open tank 2 m below the pump centreline (static suction lift = -2 m)
- Discharge into an open tank 18 m above the pump (static discharge head = +18 m)
- Pipe run: 50 m of DN80 steel pipe carrying 40 m³/h, plus 4 elbows and 1 check valve (friction losses = 3 m, from pipe friction tables)
- Both tanks open to atmosphere (no pressure head)
Total dynamic head = -(-2) + 18 + 3 + 0 = 23 m
The pump must deliver at least 23 m of head at 40 m³/h. In practice, a margin of 5–10% is added for ageing of the pump and additional fouling of the system.
Net Positive Suction Head (NPSH)
NPSH is a separate but related calculation that ensures the pump does not cavitate. NPSH Available (NPSHa) is the absolute pressure at the pump suction expressed as head, minus the vapour pressure of the liquid. NPSH Required (NPSHr) is specified by the pump manufacturer and varies with flow rate.
The rule is simple: NPSHa must exceed NPSHr by at least 0.5 m (preferably 1 m) across the entire operating range. If not, cavitation will occur, damaging the impeller and reducing performance. See our Pump Cavitation Explained guide for details.
Common mistakes when sizing pump head
- Ignoring friction losses on long pipe runs — at high flow rates, friction can easily exceed static head.
- Using nominal pipe diameter instead of internal diameter — old or fouled pipes have significantly reduced bore.
- Adding too large a safety margin — oversizing leads to operation far left of the best efficiency point, causing recirculation and shaft damage.
- Forgetting equipment pressure drops — filters, heat exchangers, and spray nozzles can contribute several metres of head.
- Confusing pressure with head — when reading manufacturer datasheets, ensure you use the correct units.