Total horsepower (THP)
Also called: THP, pump horsepower, HP rating, hydraulic horsepower.
Total horsepower (THP) is the horsepower number on most pool pump spec sheets, and the figure the federal pool-pump motor rule uses to sort motors into size classes. Roughly 1.15 total horsepower matches 0.711 hydraulic horsepower, the size where a new in-ground pump is variable-speed in practice.
Why it matters
Two federal rules use two horsepower figures. The 2021 pump rule sets its efficiency floor by hydraulic horsepower. The 2023 motor rule goes by total horsepower: motors from 1.15 to 5 must be variable-speed since September 29, 2025, and motors from 0.5 to under 1.15 from September 28, 2027. Above-ground pumps run from about ¾ to 1 total horsepower, squarely in that second class. Do not shop by the horsepower on the box. Brands multiply a motor's real horsepower by a service factor to get a bigger figure, so two pumps both labeled 1.5 HP can move very different amounts of water. Size the pump by flow in GPM.