Pump Head to Pressure Conversion
Converting head (ft or m) to pressure (psi, bar) and vice versa.
⏱️ Estimated Reading Time: 5 min
🗓️ Last Updated: 29 August 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 that a pump imparts to a fluid, expressed as the height of an equivalent column of liquid that the pump can sustain. It is a fundamental parameter in pump engineering, used to evaluate the pump’s ability to move fluid through a system.
Definition
Pump head is the vertical height of a liquid column that a pump can raise at a specific point of operation. It quantifies the energy delivered to the fluid without directly depending on the fluid’s density.
Units
- Meters (m) – metric system
- Feet (ft) – imperial system
Key Points
- Head is independent of the type of liquid. For example, a pump producing 20 meters of head will generate the same head whether pumping water, oil, or another liquid (viscosity and frictional effects aside).
- The concept of head allows engineers to compare pump performance without immediately considering fluid properties.
- Total pump head includes contributions from static lift, static discharge, friction losses
What is Pump Pressure?
Pump pressure is the force exerted by the fluid per unit area, indicating how strongly the fluid is being pushed through the system. While head measures energy in terms of height, pressure expresses it in terms of force.
Definition
Pressure is defined as the force applied per unit area: Pressure = Force / Area
Units
- Pascal (Pa) – SI unit
- Bar – common in engineering
- Pounds per square inch (psi) – imperial system
Key Points
- Unlike head, pressure is dependent on fluid density (or specific gravity). For example, the same pump producing 20 meters of head will generate a higher pressure when pumping a heavier liquid like oil compared to water.
- Pressure can be converted from head using the relation:
P = ρ × g × HWhere: ρ = fluid density (kg/m³), g = gravity (9.81 m/s²), H = pump head (m). - Pressure determines the system’s ability to overcome resistance in piping, valves, and equipment, and is crucial for avoiding issues like cavitation.
Why it matters
Pump pressure is essential for selecting appropriate piping and equipment ratings, ensuring safe and efficient operation, and verifying that the system can handle the intended flow without failure.
Formula for Converting Pump Head to Pressure
Pump head and pressure are closely related. Head represents the energy imparted to a fluid as an equivalent height of liquid, while pressure expresses the same energy as force per unit area. The fundamental relation is:
p = ρ × g × H
Where:
- p = pressure (Pa)
- ρ = fluid density (kg/m³)
- g = acceleration due to gravity (9.81 m/s²)
- H = pump head (m)
For practical engineering use, we can simplify the formulas for metric and imperial units using the fluid's specific gravity (SG):
Metric Units: p (bar) = H (m) × SG ÷ 10.2
Imperial Units: p (psi) = 0.433 × H (ft) × SG
Notes
- SG = Specific Gravity of the fluid (dimensionless, relative to water at 4°C)
- H = Head in meters for metric units or feet for imperial units
- These simplified formulas are widely used for quick pump and piping calculations without needing to convert units manually.
Example Calculation: Water at 20°C
Let’s calculate the pressure generated by a pump delivering a head of 50 meters of water at 20°C.
- Determine fluid properties:
Water density at 20°C ≈ 1000 kg/m³ → Specific Gravity (SG) = 1 - Metric calculation (bar):
Using the simplified formula:
p (bar) = H × SG ÷ 10.2
p (bar) = 50 × 1 ÷ 10.2 ≈ 4.9 bar - Imperial calculation (psi):
Convert head to feet: 50 m × 3.281 ≈ 164 ft
Using the formula:
p (psi) = 0.433 × H(ft) × SG
p (psi) = 0.433 × 164 × 1 ≈ 71 psi
Conclusion: A pump producing a head of 50 meters of water at 20°C generates approximately 4.9 bar in metric units or 71 psi in imperial units at the discharge nozzle.
- This calculation assumes negligible friction losses and is for static conditions at the discharge nozzle.
- The same approach can be applied to other liquids by using their specific gravity (SG) in place of 1.
Effect of Specific Gravity on Head-to-Pressure Conversion
For fluids other than water, the specific gravity (SG) directly affects the pressure generated for the same pump head. While head remains the same, the pressure changes proportionally with SG.
- Light fluids (SG < 1): The same head produces lower pressure. Example: Gasoline (SG ≈ 0.7) → lower discharge pressure than water for the same head.
- Heavy fluids (SG > 1): The same head produces higher pressure. Example: Sulfuric acid (SG ≈ 1.8) → higher discharge pressure than water for the same head.
Example Calculation (Sulfuric Acid):
Head = 50 m, SG = 1.8
Metric: p (bar) = H × SG ÷ 10.2 = 50 × 1.8 ÷ 10.2 ≈ 8.8 bar
Imperial: Convert 50 m → 164 ft
p (psi) = 0.433 × H(ft) × SG = 0.433 × 164 × 1.8 ≈ 128 psi
Key Point: Always account for specific gravity when converting pump head to pressure for liquids other than water. This ensures accurate system design and pump selection.
Head ↔ Pressure Conversion Calculator
Convert between pump head and pressure for any fluid
Conversion Results
Key Engineering Takeaways
- Pump head represents the energy imparted to the fluid, expressed as an equivalent liquid column height, and is not directly a measure of pressure.
- Pressure depends on the fluid density or specific gravity (SG); the same head will produce different pressures for different fluids.
- Simplified formulas can be used for quick calculations:
- Metric: p (bar) = H × SG ÷ 10.2
- Imperial: p (psi) = 0.433 × H × SG
- Always apply SG correction when working with fluids other than water to ensure accurate pump and system design.
- Use conversion tables or charts for quick reference during design, troubleshooting, or field checks.
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 |