Why This Conversion Matters
Horsepower and gallons per minute describe different pump questions. Horsepower shows power. GPM shows flow. A pump can deliver high flow at low pressure. It can also deliver lower flow at high pressure. This calculator links those values through common hydraulic formulas.
Practical Pump Planning
The tool helps during early equipment selection. Enter available horsepower, expected pressure, or total head. Then add efficiency, liquid specific gravity, and reserve margin. These values make the answer more realistic. Real pumps lose energy through friction, heat, leakage, and turbulence. Efficiency accounts for those losses.
Pressure Method
Use the pressure method when your main design value is PSI. This is useful for sprayers, washers, filtration systems, and hydraulic transfer lines. The formula uses 1714 as the standard water horsepower constant. It assumes U.S. gallons per minute and pounds per square inch.
Head Method
Use the head method when your design is based on feet of head. This is common for wells, tanks, irrigation, drainage, and building services. The formula uses 3960 as the conversion constant for water. Specific gravity adjusts the result for heavier or lighter fluids.
Reading The Result
The base result shows estimated flow before reserve. The final result applies your reserve margin. A reserve reduces the displayed design flow. It leaves horsepower available for aging, fouling, pipe friction, and changing field conditions. This is helpful when the pump will run for many hours.
Better Inputs Give Better Outputs
Use tested pressure or measured head when possible. Check pump curves from the manufacturer before buying equipment. Curves show real performance across many operating points. This calculator is an estimator, not a replacement for certified pump data. Still, it gives a strong starting point for comparison.
Useful Workflow
Run several scenarios. Compare pressure, head, and efficiency changes. Export the report when you find a useful setup. Keep the CSV for spreadsheets. Save the PDF for project notes, quotes, or client records.
Common Mistakes
Do not ignore motor loading. A rated motor may not supply full usable hydraulic power. Do not mix units inside one method. PSI belongs with 1714. Feet of head belongs with 3960. Check suction limits, pipe size, and actual pump speed before final selection carefully.