Pump Head Calculator
Pump head, formally known as Total Dynamic Head (TDH), quantifies the net mechanical energy imparted to the fluid by the pump — expressed as the equivalent height of the fluid...
Formula
Source: Engineering Toolbox, Hydraulic Institute Standards | Last reviewed: June 8, 2026
Examples
0 psi
= 115.5 ft
- P_discharge = 50
- P_suction = 0
- SG = 1
50 psi differential with water = 115.5 ft head
0 psi
= 207.9 ft
- P_discharge = 100
- P_suction = 10
- SG = 1
90 psi net rise = 208 ft for water
0 psi
= 433 ft
- P_discharge = 150
- P_suction = 0
- SG = 0.8
150 psi with 0.8 SG fluid = 433 ft head
Where is this used?
This TDH value is plotted on manufacturer pump curves to select a pump whose best efficiency point (BEP) falls near the design condition.
During factory acceptance testing per ANSI/HI 14.6, the pump vendor measures head at multiple flow points to verify the published curve — the customer's engineer independently calculates head from test gauge readings as a verification check.
In field commissioning, the startup technician records suction and discharge pressures, calculates TDH, and confirms the installed pump is operating on its curve within acceptable tolerance (typically ±5% of rated head).
Energy auditing uses TDH in conjunction with flow and power measurements to calculate wire-to-water efficiency and identify pumps that are candidates for VFD retrofits, impeller trimming, or replacement.
Condition monitoring programs track TDH over time; a gradual decline at constant flow indicates impeller wear or increasing internal recirculation, while an increase may signal downstream blockages or fouled heat exchangers.
For multi-pump configurations in series, TDH is additive — the combined head of two identical pumps in series is simply 2 × individual TDH, provided suction conditions are adequate for the second pump.
Parallel pump configurations share flow at the same head, requiring careful matching of TDH curves to avoid one pump dead-heading.
In process control, TDH influences NPSH calculations, suction-specific-speed evaluations, and determines whether a booster pump is needed in long-distance pipelines with elevation changes.
Real-World Usage Scenarios
Factory Acceptance Test Witnessing
A project engineer travels to a pump manufacturer's test facility to witness the factory acceptance test (FAT) of a 250 HP boiler feed pump per ANSI/HI 14.6 Grade 1. The test loop has calibrated pressure transmitters at the suction (5 psig) and discharge (420 psig) flanges, and the fluid is water at 80°F (SG = 1.0). Calculated head = (420 − 5) / (1.0 × 0.433) = 958 ft. The engineer compares this to the certified curve at the tested flow of 400 GPM — the curve predicts 960 ft, well within the ±2% Grade 1 acceptance band, and the pump is accepted for shipment.
Troubleshooting a Cooling Water Pump
A plant maintenance engineer is investigating why a 1,500 GPM cooling water pump is tripping on high motor amps. Field readings: suction = 8 psig, discharge = 72 psig, fluid water at 85°F (SG = 1.0). TDH = (72 − 8) / 0.433 = 148 ft. The pump curve at 1,500 GPM specifies TDH of 165 ft. The 17 ft deficit suggests the pump is running out on its curve (operating to the right of BEP at higher flow and lower head), which draws more power and trips the overload. The fix: partially close the discharge valve to shift the operating point back toward BEP, reducing flow to 1,200 GPM and bringing TDH to 160 ft — amps drop within motor nameplate rating.
Pump Head for a Glycol Chilled Water System
A commissioning agent is verifying a glycol pump for a low-temperature process cooling loop. The pump circulates 30% propylene glycol at 25°F (SG = 1.035). Gauge readings: suction = 15 psig, discharge = 95 psig. TDH = (95 − 15) / (1.035 × 0.433) = 80 / 0.448 = 179 ft. If the agent had used SG = 1.0 (water), the result would have been 185 ft — a 6 ft overestimate. The correct 179 ft TDH is used to confirm the pump is operating near its design point on the manufacturer's curve, and the glycol concentration correction is documented in the commissioning report.
Common Mistakes to Avoid
Confusing gauge pressure with absolute pressure
The pump head formula uses gauge pressure (psig), not absolute pressure (psia). If absolute pressure transducers are used, atmospheric pressure (≈14.7 psi at sea level) must be subtracted from both suction and discharge readings before computing the differential. Using psia directly overstates the ΔP by 14.7 psi, which for water translates to an error of approximately 34 ft of head — enough to misdiagnose a pump as healthy when it is severely underperforming.
Neglecting gauge elevation correction
When suction and discharge pressure gauges are mounted at different elevations, the height difference must be added to the calculated head. A discharge gauge located 3 ft above the suction gauge will read approximately 1.3 psi lower than it would at the same elevation (for water). Failing to correct for gauge elevation produces head errors that compound with friction loss calculations, leading to incorrect NPSH margin assessments.
Using nominal SG instead of measured SG at operating temperature
Fluid specific gravity changes with temperature — water at 200°F (93°C) has an SG of approximately 0.96, not 1.0. Using SG = 1.0 for hot water produces a 4% error in calculated head. For hydrocarbon services, SG at pumping temperature can differ by 5-15% from the standard 60°F reference value. Always measure SG at the actual pumping temperature or use temperature correction tables.
Industry Standards Referenced
Frequently Asked Questions
What is the relationship between total head and pressure?
Total head (ft) = Pressure (psi) × 2.31 / SG. For water (SG=1), 1 psi = 2.31 ft of head. This relationship is fundamental to pump selection — a pump that produces 100 psi with water is said to have 231 ft of head.
Should I use gauge or absolute pressure?
Gauge pressure (psig) is correct for this calculation because the pressure differential across the pump is what matters. The atmospheric pressure cancels out since both suction and discharge gauges reference the same atmospheric pressure.
What if the suction pressure is negative?
Negative suction pressure (vacuum) is common when pumping from below the pump centerline. Enter it as a negative value. The formula still works: head = (P_discharge − (−5)) / (SG × 0.433). Negative suction increases the total head the pump must produce.
How does specific gravity affect the pump head calculation?
Specific gravity inversely affects the calculated head. For a given ΔP, a heavier fluid (higher SG) produces less head in feet because a shorter column of dense fluid generates the same pressure at the base. For example, 100 psi across a pump with SG = 1.2 yields 100 / (1.2 × 0.433) = 192 ft, versus 231 ft for water — a 17% reduction. This is critical when pumping brines, glycol solutions, or hydrocarbons where SG differs significantly from 1.0.
Do I need to account for velocity head between suction and discharge?
For most industrial pump applications with equal suction and discharge pipe diameters, velocity head cancels out. However, when suction and discharge nozzle sizes differ (common with end-suction pumps), the velocity head difference should be added: Δvelocity head = (V_d² − V_s²) / 2g, where V is flow velocity in ft/s and g is 32.174 ft/s². This correction is typically under 1–2 ft and is often neglected for general troubleshooting, but should be included for precision performance testing per ANSI/HI 14.6 Grade 1.
Reviewed for accuracy
Reviewed against ANSI/HI 14.6, ISO 9906, and API 610 standards · Last reviewed: June 8, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.