Head Pressure Calculator: Convert PSI to Feet of Head
This tool allows you to convert known system pressure (in psi) into equivalent head (in feet). It's useful for pump selection, fluid handling design, and verifying system parameters based on pressure measurements.
Understanding Head Pressure in Pump Systems
In pump system design and troubleshooting, the term "head" refers to the height a pump can raise a liquid, expressed in feet or meters. When a system’s pressure is known in PSI (pounds per square inch), it’s often necessary to convert that value into head pressure to match pump specifications or calculate flow requirements. This calculator simplifies that process by converting PSI into feet of head, using fluid density for accuracy.
PSI to Head Conversion Formula
The standard conversion formula is:
Head (ft) = Pressure (psi) ÷ (0.4335 × Specific Gravity)
- 0.4335 represents the psi exerted by a 1-foot column of water at 60°F.
- Specific Gravity (SG) is the fluid’s density compared to water (SG = 1.0 for water).
By dividing the PSI by this constant and correcting for SG, the result is the fluid's equivalent column height—i.e., head pressure.
Example Calculations
Example 1: You have a system pressure of 65 psi and the fluid is water (SG = 1.0).
Head = 65 / (0.4335 × 1.0) = 149.94 ft
Example 2: A chemical system operates at 100 psi with a fluid SG = 1.3.
Head = 100 / (0.4335 × 1.3) = 177.33 ft
Unit Conversion Table
This table shows approximate conversions from PSI to Head for water and common SG values:
| Pressure (psi) | Head @ SG=1.0 (ft) | Head @ SG=1.2 (ft) | Head @ SG=1.5 (ft) |
|---|---|---|---|
| 10 psi | 23.07 ft | 19.22 ft | 15.38 ft |
| 25 psi | 57.68 ft | 48.06 ft | 38.46 ft |
| 50 psi | 115.37 ft | 96.13 ft | 76.92 ft |
| 75 psi | 173.05 ft | 144.19 ft | 115.38 ft |
| 100 psi | 230.74 ft | 192.26 ft | 153.84 ft |
Why Convert PSI to Head?
- Pump curves are typically plotted using head (not PSI)
- Pump selection requires understanding total dynamic head (TDH)
- System sizing often uses vertical height + friction losses in feet
- Code compliance (fire systems, HVAC, etc.) may require head-based specs
Frequently Asked Questions
Can I use this calculator for any fluid?
Yes, as long as you know the specific gravity. Most water-based fluids are near 1.0. Heavier chemicals (like sulfuric acid) or lighter ones (like gasoline) need adjusted SG values.
What if I don’t know the fluid’s SG?
Use 1.0 for water, or consult a chemical data sheet (MSDS). Many engineering handbooks also provide SG values.
How accurate is the 0.4335 constant?
This value is based on fresh water at 60°F. For precise engineering in extreme temperatures or with compressible fluids, you may need temperature or pressure correction.
Can I convert back from head to PSI?
Yes. Just reverse the formula: PSI = Head × 0.4335 × SG.
Does elevation or altitude affect this calculation?
Not significantly for liquids. This formula is based on incompressible fluids. For gas systems, pressure and head relationships are more complex and require different equations.
Common Applications of Head Pressure
- Municipal water supply — Typical head ranges from 50–200 ft
- Irrigation systems — Head must overcome pipe length and elevation
- Fire protection systems — NFPA specifies minimum discharge heads
- Industrial pump selection — Pump curves rated in feet of head
- Chillers and cooling towers — Require system pressure converted to feet
Design and Safety Considerations
- Ensure system piping is pressure-rated for calculated discharge
- Include safety margins for variable head loss (valves, fittings, etc.)
- Size pumps to operate near their Best Efficiency Point (BEP)
- Install pressure gauges and head monitoring where appropriate
- Use VFDs to adjust for dynamic system demands
Conclusion
Understanding how to convert PSI to feet of head allows engineers and technicians to bridge the gap between pressure-based measurements and pump performance data. Whether designing a municipal system, industrial fluid loop, or residential booster, knowing your required head is key to optimal pump selection and system reliability.