About this tool
Power-to-Weight Ratio Calculator is a free, in-browser tool that turns an engine's power and a vehicle's weight into the single number enthusiasts use to compare acceleration potential across very different cars. Enter power in horsepower or kilowatts and weight in pounds or kilograms; everything is computed locally as you type and nothing is uploaded.
Power is first converted to watts (1 hp = 745.7 W, 1 kW = 1000 W) and weight to kilograms (1 lb = 0.453592 kg). The headline figure is W/kg = watts ÷ kilograms. From the same inputs it also derives hp per US ton (hp × 2000 ÷ pounds), hp per 1000 lb (hp × 1000 ÷ pounds) and kW per tonne — which is numerically identical to W/kg — so you can quote whichever convention your region prefers.
Because it strips out units, the ratio lets you line up a light hatchback against a heavy muscle car fairly. The tool also prints a rough performance class band, from economy commuter up to hypercar, based on the W/kg result — a quick sanity check, not a lap-time prediction.