Pump Head to Pressure Conversion
Converting head (ft or m) to pressure (psi, bar) and vice versa.
Updated: 20-Aug-2025
In pump engineering, two common terms often create confusion: head and pressure. Although related, they are not the same. Pump manufacturers usually specify performance curves in terms of head (meters or feet), while process engineers frequently deal with pressure (bar, psi, or Pa). To properly size, select, and analyze pumps, it is essential to understand how to convert pump head into pressure.
This guide explains the theory, presents conversion formulas, provides a worked-out example using water, discusses the effect of specific gravity, and includes a conversion table of head vs. pressure.
What is Pump Head?
Pump head represents the energy imparted by the pump to the fluid, expressed as an equivalent height of liquid column.
- Definition: Head is the vertical height of a liquid column that a pump can raise at a given point of operation.
- Units: meters (m) or feet (ft).
- Key point: Head is independent of fluid density. A pump will produce the same head for water, oil, or any liquid (neglecting viscosity effects), but the corresponding pressure will change.
What is Pump Pressure?
Pressure is the force per unit area exerted by the fluid.
- Definition: Pressure = Force / Area.
- Units: Pascal (Pa), bar, or pounds per square inch (psi).
- Unlike head, pressure is directly dependent on the density (or specific gravity) of the fluid.
Formula for Converting Pump Head to Pressure
The fundamental relation between head (H) and pressure (p) is:
p = ρ × g × H
Where:
- p = pressure (Pa)
- ρ = fluid density (kg/m³)
- g = acceleration due to gravity (9.81 m/s²)
- H = head (m)
For practical engineering calculations, the formula can be simplified as:
p (bar) = H × SG / 10.2
p (psi) = 0.433 × H × SG
Example Calculation (Water at 20°C)
Suppose a pump delivers a head of 50 meters of water. What is the pressure at the discharge nozzle?
- Water density ≈ 1000 kg/m³ → SG = 1
- Using the formula:
p (bar) = (50 × 1) / 10.2 ≈ 4.9 bar - Alternatively, in psi:
50 m ≈ 164 ft
p (psi) = 0.433 × 164 × 1 ≈ 71 psi
Result: A head of 50 m water corresponds to ~4.9 bar or ~71 psi.
Effect of Specific Gravity on Conversion
For fluids other than water, specific gravity (SG) modifies the pressure:
- Light fluids (SG < 1): same head produces lower pressure (e.g., gasoline SG ≈ 0.7).
- Heavy fluids (SG > 1): same head produces higher pressure (e.g., sulfuric acid SG ≈ 1.8).
Example: 50 m head for sulfuric acid (SG = 1.8):
p (bar) = (50 × 1.8) / 10.2 ≈ 8.8 bar
Head ↔ Pressure Conversion Calculator
Convert between pump head and pressure for any fluid
Conversion Results
Key Engineering Takeaways
- Pump head is a measure of energy, not pressure.
- Pressure conversion depends on fluid density (SG).
- Use simplified formulas for quick checks:
- p (bar) = H × SG / 10.2
- p (psi) = 0.433 × H × SG
- Always apply SG correction for non-water fluids.
- Refer to conversion tables for quick reference in design and troubleshooting.
Conversion Table – Water Head vs. Pressure
| Head (m) | Head (ft) | Pressure (bar) | Pressure (psi) |
|---|---|---|---|
| 1 | 3.28 | 0.098 | 1.42 |
| 5 | 16.4 | 0.49 | 7.1 |
| 10 | 32.8 | 0.98 | 14.2 |
| 20 | 65.6 | 1.96 | 28.4 |
| 30 | 98.4 | 2.94 | 42.7 |
| 40 | 131 | 3.92 | 56.9 |
| 50 | 164 | 4.90 | 71.1 |
| 75 | 246 | 7.35 | 106.7 |
| 100 | 328 | 9.81 | 142.2 |
| 150 | 492 | 14.7 | 213.4 |
| 200 | 656 | 19.6 | 284.5 |