PSI to Feet of Head Converter
Pump performance curves are almost universally presented in feet (or meters) of head rather than pressure units, because head is independent of fluid density while pressure is...
Formula
Source: Engineering Toolbox, Hydraulic Institute Standards | Last reviewed: June 7, 2026
Examples
50 psi
= 115.5 ft
- SG = 1
Water at 50 psi
50 psi
= 144.4 ft
- SG = 0.8
Kerosene (SG 0.8)
100 psi
= 231 ft
- SG = 1
Water at 100 psi
Quick Reference Table
| psi | ft head |
|---|---|
| 10 | 23.1 |
| 20 | 46.2 |
| 30 | 69.3 |
| 50 | 115.5 |
| 100 | 231 |
| 150 | 346.5 |
| 200 | 462 |
Where is this used?
Water and wastewater treatment plants rely on it when selecting vertical turbine pumps for deep-well applications — a well pump must overcome 300 ft of static lift plus friction losses, expressed as total dynamic head (TDH), while the pump curves from manufacturers like Goulds, Flowserve, and Sulzer are plotted in feet.
Converting the required discharge pressure from psi to feet lets the engineer overlay the system curve directly.
In building services, HVAC hydronic loop design requires converting the closed-loop pressure drop (often calculated in psi by piping software like Pipe-Flo or AFT Fathom) to feet of head so that the circulator pump selection matches the system resistance curve.
A common error is to take the boiler or chiller pressure drop in psi, convert to feet assuming water, and select a pump without recognizing that hot water at 180°F (SG ≈ 0.97) or a glycol-water mixture (SG ≈ 1.02–1.05 for 30–50% propylene glycol) requires SG correction — misapplied, this leads to a pump that is 3–5% undersized for glycol systems.
In the oil and gas sector, pipeline booster pump stations handle crude oils with SG ranging from 0.79 (light condensate) to 0.95+ (heavy crude) and must convert pipeline pressure drop in psi to head in feet for pump curve evaluation, while also correcting for viscosity using the Hydraulic Institute's viscous correction charts (ANSI/HI 9.6.7).
Chemical process engineers designing reactor cooling loops with heat transfer fluids like Therminol VP-1 (SG varying from 0.89 at 100°F to 0.76 at 600°F) must convert design pressures at operating temperature using the density at temperature, not ambient SG from the manufacturer's SDS.
In mining, tailings slurry pumps handling mixtures with SG up to 1.8 require careful head conversion: the pressure rating of the pump casing in psi converts to much less head than for water, meaning the pump may not generate enough head to overcome the static lift of a dense slurry column.
Field commissioning engineers use the conversion in reverse — reading a pressure gauge in psi at the pump discharge, dividing by 2.31 and multiplying by SG, to verify that the pump is operating on its curve at the expected flow rate.
This on-site validation is a standard punch-list item before mechanical completion sign-off.
Real-World Usage Scenarios
Boiler Feedwater Pump Selection
A 500-hp firetube boiler requires feedwater at 250 psig from a deaerator operating at 5 psig and 227°F. The system resistance includes 15 psi of piping and valve losses, 5 psi of economizer drop, and 230 psi of boiler drum elevation gain equivalent to approximately 60 ft of static head. For water at 227°F (SG = 0.955), the total dynamic head is (250 + 15 + 5 - 5) × 2.31 / 0.955 + 60 = 265 × 2.31 / 0.955 + 60 ≈ 700 ft. The pump must be selected for 700 ft TDH — selecting based on 265 psi × 2.31 = 612 ft without SG correction would result in a pump that starves the boiler at full load, potentially causing tube overheating.
Glycol Chilled Water Loop Pump Verification
A data center chilled water loop circulates 30% propylene glycol at 45°F (SG = 1.026). The design pressure drop across the piping and coils is 65 psid. Converting to head: 65 × 2.31 / 1.026 = 146.4 ft. A field commissioning agent measures only 140 ft at the pump differential pressure transmitter, suspects underperformance, and orders a pump rebuild. In reality, the glycol concentration was mixed at 35% (SG = 1.030) and the actual pressure drop matches the design head — the SG was never verified during commissioning. A density check on a glycol refractometer resolves the discrepancy without invasive pump work.
Hydrocarbon Pipeline Booster Station
A 12-inch crude oil pipeline transports 60,000 BPD of 32°API crude (SG = 0.865) across a 50-mile segment with a 1,200-ft elevation rise. The hydraulic simulation reports a required pressure boost of 720 psi. Converting to pump head: 720 × 2.31 / 0.865 = 1,923 ft. A 4-stage horizontal split-case pump with 500 ft/stage is selected. If the conversion had used SG = 1.0, the calculated head would have been only 1,663 ft — a 14% shortfall that would have required a costly mid-project pump change order or the addition of an intermediate booster station.
Common Mistakes to Avoid
Forgetting to apply specific gravity
The most frequent pump selection error: converting 100 psi to 231 ft of head using the 2.31 constant without dividing by SG. For a fluid with SG = 1.2 (brine, slurry), the true head is only 192.5 ft — a 17% overestimate that leads to selecting a pump incapable of overcoming the actual system resistance. Always locate the fluid SG at operating temperature from the process data sheet or SDS before converting.
Metric-imperial unit confusion
European pump curves are plotted in meters of head (1 m = 3.281 ft) and European system calculations are often in bar or kPa. A common mistake is applying the 2.31 constant to a value in bar instead of psi. The metric equivalent is h(m) = 10.2 × P(bar) / SG. Mixing metric pressure with imperial head constants produces nonsensical results — verify the unit system before selecting the formula.
Using cold-water SG for hot service
Pump selection for a boiler feedwater pump at 220°F requires SG ≈ 0.957 (not 1.0). Converting the system pressure drop of 150 psi to feet of head with SG = 1.0 gives 346.5 ft. With the correct SG, the head is 150 × 2.31 / 0.957 = 362 ft. The 15.5 ft difference may exceed the pump's NPSH margin or push the operating point off the right side of the curve into an unstable region.
Neglecting NPSH implications of SG changes
Net Positive Suction Head (NPSH) is always expressed in feet of the pumped liquid, not in pressure units. When converting the available suction pressure to NPSHA, boiling-point elevation and vapor pressure must be considered — but the head conversion itself is independent of SG (since NPSH is head, not pressure). Engineers sometimes erroneously divide the suction pressure by SG before computing NPSHA, which double-corrects and produces a falsely optimistic margin.
Industry Standards Referenced
Frequently Asked Questions
Why use head instead of pressure?
Head is a measure of energy per unit weight, so a pump rated for 100 ft of head can pump 100 ft of water, 100 ft of kerosene, or 100 ft of sulfuric acid to the same height — even though the discharge pressure differs. This makes pump curves universal across fluids.
What is the formula for SG?
SG (specific gravity) is the ratio of fluid density to water density (1000 kg/m³ or 62.4 lb/ft³). For water at 4°C, SG = 1.0 exactly.
What about feet-to-meters of head?
1 ft of head = 0.3048 m of head. A 100 ft pump rated for water moves the same fluid column as a 30.48 m pump, regardless of fluid density.
How does temperature affect the head conversion?
Water density decreases as temperature rises — at 200°F, water density drops to approximately 60.1 lb/ft³ (SG ≈ 0.963), which changes the conversion constant from 2.31 to roughly 2.40. For hot-water circulating pumps, always use the SG at the pump suction temperature, not the cold-fill density. The error from ignoring temperature is about 4% at 200°F, which can push a pump outside its allowable operating region on the curve.
Why is my pump discharge pressure lower than expected for the rated head?
If SG < 1.0 (light hydrocarbons, hot water, solvents), the same head produces lower pressure. For example, a pump rated 200 ft pumping naphtha (SG = 0.72) will only develop about 62 psig at the discharge flange — not the 86.6 psig expected for water. Conversely, a brine pump (SG = 1.2) producing 200 ft of head will show about 104 psig. Always convert expected head to pressure using the correct SG before concluding the pump is underperforming.
Reviewed for accuracy
Reviewed against ANSI/HI 14.6 and ISO 9906 standards · Last reviewed: June 7, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.