Pump Water Horsepower
Also known as WHP · hydraulic horsepower
Worked example: 20 kW into 1.2 SG brine at 15 m head → 6798.1 L/min — press Try an example to run it live, then adjust anything.
Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Try different units for next level excitement!
Water power →
UniversityFluid Mechanics, HVAC & Refrigeration
Test your skills in the Exam Room: new numbers every attempt — free lessons for students, no sign-up, just pure learning. Find 1 more lesson on this formula.
share your results
Pump Water Horsepower explained
Water horsepower is the honest output of a pump: the weight of liquid lifted per second times the height it is lifted. In US customary units that reduces to gpm × ft × SG ÷ 3960, where the 3960 is just 33 000 ft·lbf/min per horsepower divided by 8.33 lb per gallon of water. Pump 500 gpm to 100 ft of head on water and you are delivering 500 × 100 × 1.0 / 3960 ≈ 12.6 hp to the liquid — this calculator works in exact SI (ρgQH with g = 9.80665) and returns 12.64 hp, the small difference being the rounding baked into 3960.
The specific-gravity term is where people come unstuck. Head in feet is independent of density, but power is not: the same pump moving 1.2 SG glycol brine to the same 100 ft of head needs 20% more horsepower even though the gauge pressure and the curve point are unchanged. Size the motor for the coldest, densest fluid the system will ever see, including a winter glycol charge that maintenance may add years later.
Pump Water Horsepower formula
- = Water horsepower (W)
- = Flow rate (L/min)
- = Total head (m)
- = Specific gravity
Missing one of these? Work it out first, then come back
- Water horsepower — Pump Brake Horsepower, Condenser Water Flow Rate
- Flow rate — Pump Brake Horsepower, Hazen–Williams Head Loss
- Total head — Pump Brake Horsepower, Hydraulic Power (P = ρgQh)
- Specific gravity — Pump Brake Horsepower, Valve Flow Coefficient (Cv)