Pump Power Calculator
Plan your water tank & vessels project with our free pump power calculator. Get precise measurements, material lists, and budgets.
Formula
WHP = Q x H x SG / 3960 | BHP = WHP / Efficiency
Water Horsepower equals the flow rate (GPM) times total dynamic head (ft) times specific gravity, divided by 3960. Brake Horsepower divides WHP by pump efficiency to account for internal losses. Multiply BHP by 0.7457 to get kilowatts, then divide by motor efficiency for electrical input power.
Worked Examples
Example 1: Irrigation Pump Sizing
Problem: Size a pump for 100 GPM at 50 feet TDH with 70% pump efficiency, pumping water (SG = 1.0).
Solution: WHP = 100 x 50 x 1.0 / 3960 = 1.26 HP\nBHP = 1.26 / 0.70 = 1.80 HP\nkW = 1.80 x 0.7457 = 1.34 kW\nElectrical = 1.34 / 0.90 = 1.49 kW
Result: 1.80 BHP (select 2 HP motor), 1.49 kW electrical input
Example 2: Industrial Chemical Transfer Pump
Problem: Calculate power for pumping brine (SG = 1.2) at 200 GPM against 80 feet TDH with 65% efficiency.
Solution: WHP = 200 x 80 x 1.2 / 3960 = 4.85 HP\nBHP = 4.85 / 0.65 = 7.46 HP\nkW = 7.46 x 0.7457 = 5.56 kW\nAnnual cost = (5.56/0.90) x 8 x 365 x 0.12 = $2,165
Result: 7.46 BHP (select 10 HP motor), annual energy cost about $2,165
Frequently Asked Questions
How do you calculate pump power in horsepower?
Pump power is calculated in two steps. First, find the Water Horsepower (WHP) using WHP = Q x H x SG / 3960, where Q is flow in gallons per minute, H is total dynamic head in feet, and SG is specific gravity of the liquid. Then divide WHP by the pump efficiency (as a decimal) to get Brake Horsepower (BHP), which is the actual shaft power the motor must deliver. The constant 3960 converts the units so the result is in horsepower.
What is a typical pump efficiency?
Centrifugal pump efficiency typically ranges from 60% to 85% at the best efficiency point (BEP), depending on pump size and design. Small residential pumps may be 50-65% efficient, medium commercial pumps 65-80%, and large industrial pumps 80-90%. Efficiency drops significantly when operating far from the BEP flow rate. Positive displacement pumps like gear and diaphragm pumps typically achieve 80-95% efficiency. Always select a pump that operates near its BEP for the required flow and head.
How do I estimate pump operating costs?
Multiply the electrical power consumption in kilowatts by the daily run hours, then by 365 days and your electricity rate per kWh. Electrical power equals brake horsepower times 0.7457 divided by motor efficiency (typically 0.90 to 0.95). For example, a 10 BHP pump with a 90% efficient motor draws 8.29 kW. Running 8 hours daily at $0.12/kWh costs about $2,905 per year. Variable frequency drives (VFDs) can reduce costs by 30-50% in variable flow applications.
How accurate are the results from Pump Power Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
Is Pump Power Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.