Pump Calculator

TDH represents the total equivalent height water must be lifted, combining physical elevation rise (static head) plus friction pressure losses from pipe walls, fittings, bends, and valves.

Thicker, more viscous fluids (oils, sludge, syrups) increase friction losses and require higher brake horsepower to pump the same volume. For non-water fluids, multiply by the fluid's specific gravity.

Water horsepower (WHP) is the theoretical power needed to move the fluid. Brake horsepower (BHP) is the actual power the motor must deliver, accounting for mechanical and hydraulic losses in the pump.

The constant 3960 converts the units: (GPM × feet) / (33,000 ft-lb/min per HP × 8.33 lb/gal) = (GPM × feet) / 3960. It unifies gallons, feet, and horsepower.

Measure static head (vertical lift from water surface to discharge point) and add friction losses (calculated using pipe length, diameter, fittings, and flow rate using Hazen-Williams or Darcy-Weisbach equations).

Centrifugal pump efficiency ranges from 50% for small residential pumps to 85%+ for large industrial pumps. The best efficiency point (BEP) varies by impeller design and operating conditions.

Specific gravity (SG) adjusts for fluid density. Water has SG = 1.0. Heavier fluids (SG > 1) require more horsepower; lighter fluids (SG < 1) require less. Multiply WHP by SG.

Always round up to the next standard motor size and add 10-20% safety margin for starting torque and load fluctuations. For 2.60 BHP, select a 3 HP or 5 HP motor depending on duty cycle.

Affinity laws relate speed changes to flow, head, and power: Q₂/Q₁ = N₂/N₁, H₂/H₁ = (N₂/N₁)², P₂/P₁ = (N₂/N₁)³. Doubling speed quadruples head and multiplies power by eight.

Multiply GPM by 3.785. For example, 120 GPM × 3.785 = 454.2 LPM.

Static head is the vertical distance between suction and discharge water levels. Dynamic head includes static head plus all friction losses in pipes, valves, and fittings at the operating flow rate.

Larger pipes reduce friction losses, lowering TDH and reducing required BHP. Undersized pipes increase friction, raising TDH and potentially causing cavitation at the pump suction.

Cavitation occurs when suction pressure drops below the fluid's vapor pressure, forming bubbles that collapse violently. Prevent it by maintaining adequate suction head (NPSH available > NPSH required).

Net Positive Suction Head (NPSH) is the minimum pressure at the pump inlet needed to prevent cavitation. NPSH Available must always exceed NPSH Required by the pump manufacturer.

At higher elevations, atmospheric pressure decreases, reducing NPSH available. For every 1,000 feet of elevation, atmospheric pressure drops about 1 psi (0.7 kPa), potentially requiring a larger suction pipe or lower pump placement.

Open-loop systems (irrigation, drainage) draw from a source and discharge elsewhere. Closed-loop systems (HVAC, chilled water) recirculate fluid continuously, requiring less makeup water but careful thermal management.

Flow rate (GPM) = Velocity (FPS) × Cross-sectional area (sq. in.) × 0.449. Or use: Q = 2.448 × d² × v where d is pipe ID in inches.

For centrifugal pumps, power increases roughly linearly with flow rate at constant head. For positive displacement pumps, power is more directly proportional to both flow and pressure.

Measure the well depth, desired flow rate, and add friction losses for drop pipe and fittings. Use this calculator to find BHP, then select a submersible or jet pump rated for at least that capacity.

The service factor (SF) is the ratio of maximum continuous power to rated power. A motor with 1.15 SF can handle 15% overload continuously. Use SF when selecting motors for variable-load applications.

Hot water reduces fluid density (lower SG), slightly reducing BHP but also reducing NPSH available. Water at 100°F has SG ≈ 0.993 vs 1.0 at 60°F. Steam systems require special pump designs.

Optimize impeller trimming to match actual duty point, reduce pipe friction with larger diameters, eliminate unnecessary fittings, maintain proper alignment, and replace worn wear rings and seals.

The Pump Calculator uses verified mathematical formulas processed entirely in your browser. Calculator inputs and results are never sent to external servers. We do use Google Analytics and AdSense for standard website operation — see our Privacy Policy for details.

Yes. All calculations happen locally in your browser. We never store, transmit, or log any input data you enter into the calculator.

Double-check that all inputs are valid numbers within reasonable ranges. If you believe there is an error, please contact us with your input values and we will investigate.