0 ft
- In metres
- 0 m
- Friction component
- 0 ft
- Static component
- 0 ft
- Hydraulic power
- 0 kW
Pump Sizing Calculator
Build the suction side, build the discharge side, get TDH and a recommended motor in one place. NPSH-available is the cavitation guard most quick calcs skip.
Design point
Suction side
Pipe segments
Fittings on this segment 3
Fittings & valves
Tap to add. Equivalent length and Σ K both update live and feed the friction calc.
3 added Σ K 0.97 Σ L/D 41Elbows
1000Tees
00Valves
10000000000Transitions
0000Entry / Exit
010
Friction 1 ft v_peak 4.54 ft/s
Discharge side
Pipe segments
Fittings on this segment 5
Fittings & valves
Tap to add. Equivalent length and Σ K both update live and feed the friction calc.
5 added Σ K 4.42 Σ L/D 198Elbows
3000Tees
00Valves
10001000000Transitions
0000Entry / Exit
000
Friction 9.53 ft v_peak 6.54 ft/s
Motor sizing & energy
NEMA standard motor; energy cost based on shaft power and motor efficiency.
Shaft power
0.88kW
1.18 HP at pump shaftRecommended motor
1.5HP
Next-up NEMA, calc 1.29 HPAnnual energy
1,919kWh
at η_m = 0.92Annual energy cost
$269
per yearNPSH available — cavitation guard
Compare NPSH_a to the pump's NPSH_required. Margin should be at least 1 m / 3 ft.
NPSH available
27.23ft
8.3 m
· OK if pump NPSH_r < this minus safety marginPump curve overlay — find your operating point
Paste a pump curve from the manufacturer's datasheet. We fit H = a − b·Q², draw the system curve from your static head and friction, and mark where they cross. Off-BEP operation wears bearings, oversizes motors, and burns electricity — this is the chart that catches it.
How this works
Total Dynamic Head: TDH = hstatic + hfriction + hpressure Hydraulic power: Phyd = ρ · g · Q · H Wire-to-water efficiency: η = ηp × ηm NPSH available: NPSHa = (Patm − Pvap) / (ρg) − hsuct,lift − hsuct,friction
Pump sizing is a head + flow problem. The system curve (TDH vs Q) intersects the pump curve at the operating point. Get TDH wrong and the pump runs off-BEP — wear, vibration, energy waste. The usual culprit is under-counted fittings on the discharge side; the counter here keeps that honest.
NPSH is the harder half. A pump that's been running fine for years can start cavitating when the supply tank drops, the fluid heats up, or someone closes a partly-open suction valve. The check here is the same one a vendor's selection software performs.
| Small (≤5 HP) | Medium (5-50 HP) | Large (>50 HP) | |
|---|---|---|---|
| Pump η_p | 55-65% | 65-75% | 75-85% |
| NEMA Premium motor η_m | 85-90% | 91-94% | 94-96% |
| Wire-to-water | ~50% | ~65% | ~80% |
Common questions
What is TDH and why does it matter?
Total Dynamic Head — the head the pump must develop. It equals static lift plus friction losses plus discharge pressure (converted to head). Pump curves are plotted with TDH on the y-axis vs flow on the x-axis; you size the pump where its curve crosses the system curve at design flow.
How is NPSH-available calculated?
NPSH_a = (P_atm − P_vapor) / (ρg) − suction-lift − suction-friction. We use atmospheric pressure (101.325 kPa default), water vapor pressure (2.34 kPa @ 20 °C default — change for hot water!), and the suction-side losses computed above. The pump's NPSH_required must be less than NPSH_a or the pump will cavitate.
Why are pump and motor efficiencies separate?
The pump converts shaft power to fluid power (η_p, typically 50-80%). The motor converts electrical power to shaft power (η_m, typically 85-95%). Total wire-to-water efficiency is η_p × η_m. We expose them separately so you can model upgrades independently.
What does "next-up NEMA size" mean?
Standard motor sizes in HP. We pick the smallest standard that meets the calculated motor power. Sizing exactly at the calculated HP is an anti-pattern: motor service factor and starting current both want some headroom.