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DIY Cost Tools

DIY Cost Tools

Power-to-Weight Ratio Calculator

Compare vehicle power with weight in horsepower per US ton, watts per kilogram, and kilograms per kilowatt.

Use the units shown beside each field. Decimal and scientific notation are accepted for non-integer fields; blanks, commas, fractions and non-finite entries are rejected.

Crank horsepower per US ton171.4285714 hp/ton
Estimated wheel horsepower255 hp
Wheel watts per kilogram119.7761816 W/kg
Kilograms per wheel kilowatt8.348905323 kg/kW

The displayed results apply to the default example. Enable JavaScript to calculate other inputs.

How to use this calculator

  1. Replace the example values with measurements or ratings for the exact vehicle, circuit, component or system.
  2. Keep every value in the labeled unit and use manufacturer data where available.
  3. Select Calculate, then review the result together with the limitations and safety notes.

Formula and method

Crank hp/ton = horsepower ÷ (pounds ÷ 2,000). Estimated wheel power applies the entered loss; W/kg converts horsepower and pounds to SI.

Calculations run in your browser. Results are hidden whenever an input changes or validation fails, preventing an older result from being mistaken for a new calculation.

Worked example

Engine power = 300 hp; Vehicle weight = 3500 lb; Estimated drivetrain loss = 15 %. The calculator returns Crank horsepower per US ton = 171.4285714 hp/ton; Estimated wheel horsepower = 255 hp; Wheel watts per kilogram = 119.7761816 W/kg; Kilograms per wheel kilowatt = 8.348905323 kg/kW.

The worked example uses the same defaults shown in the interface, allowing the formula and displayed result to be checked together.

Limitations and safety

Drivetrain loss is not a fixed universal percentage and measured power varies by test method and conditions. This ratio does not predict acceleration by itself.

This is an educational planning model. Confirm ratings, tolerances, code requirements and safe procedures with manufacturers and qualified professionals before purchasing, modifying, wiring or operating equipment.

Frequently asked questions

Should curb weight include the driver?

For performance comparison, use the actual running weight you want to evaluate, including occupants, fuel and cargo when relevant.

Why does the calculator reject my entry?

Each field shows its supported range. Whole-number fields reject decimals, and all fields reject blanks, words, comma-formatted numbers, fractions and non-finite values.

How should I use the displayed precision?

Keep extra digits while checking the calculation, then round to the precision supported by the measurements, component tolerances and published ratings.

Review notes and reference

Reviewed October 4, 2026. The formula and default example were checked together. The script was tested for defaults, input boundaries, invalid formats, condition-specific errors and recovery after an error. Reference: NHTSA vehicle and tire safety guidance. Explanations and examples are original.

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