Why “HP” doesn’t equal “GPM” (and what *does*)
Pump horsepower does not directly tell you how many gallons per minute a pool pump will move. Horsepower describes motor capacity, while actual flow depends on the pump design and the resistance created by the plumbing system.
Older single-speed pump labels often list both horsepower and service factor. Multiplying those numbers gives Total Horsepower, or THP. THP is more useful than the nameplate horsepower alone when comparing replacement motors or pump classes.
Total dynamic head represents the resistance the pump must overcome. Long plumbing runs, small pipe, elbows, valves, filters, heaters, water features, and elevation changes all increase resistance and can reduce flow.
Voltage multiplied by amperage gives a rough electrical input estimate, but motors are not perfectly efficient and AC power calculations can involve power factor. Use the optional watt estimate as a reality check, not a substitute for manufacturer specifications.