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Pump Sizing Calculator

GPM + TDH → BHP · Motor HP · kW · NPSH

When to use: Use to determine pump brake horsepower (BHP) and select the standard motor size from design flow (GPM) and total dynamic head (TDH). TDH includes static lift, friction losses, and pressure requirements. Applies to chilled water, hot water, domestic water, and process fluid systems. The formula is: BHP = GPM × TDH × SG / (3960 × pump efficiency).

Pump Parameters
Peak operating flow
GPM
Static + friction + pressure
ft
1.0 = water
SG
Typically 90–95%
%
Selected Motor Size
5
HP (standard NEMA size)
Results
Water HP (WHP)2.02 HP
Brake HP (BHP)2.81 HP
Input / Shaft HP3.05 HP
Input Power2.27 kW
NPSH Required (est.)11.0 ft
References
BHP = GPM × TDH × SG / (3960 × η)
ASHRAE Handbook – HVAC Systems & Equipment
NEMA standard motor sizes (HP)
Add 10–20% safety factor to motor selection