How to use this calculator
Enter a documented power figure and select its stated unit. Enter total vehicle mass for the condition you want to compare, including driver, fuel and cargo when applicable. Read the power-per-mass ratios and their inverse forms. For comparisons, use the same power measurement basis and the same loading convention for both vehicles.
This is a ratio of the supplied quantities, not a prediction of acceleration, top speed, lap time or quarter-mile performance. Tire traction, gearing, the power curve, shifting and road loads are not modeled. It does not determine vehicle safety, towing capacity or eligibility under any licensing or competition rule.
The formula
A worked example
A hypothetical 300 mechanical hp vehicle at 1,500 kg has 300 ÷ 1.5 = 200 hp per metric tonne. Its power is 223.71 kW, giving 149.14 kW/t, 11.02 lb/hp and 6.71 kg/kW. Adding 150 kg without changing power gives 181.82 hp/t: a 10% mass increase reduces power per mass by about 9.09%, not 10%.
Same 300 hp, different loaded mass
Original hypothetical examples using mechanical hp and metric tonnes.
| Mass (kg) | Power (hp) | Ratio (hp/t) |
|---|---|---|
| 1,200 | 300 | 250.00 |
| 1,500 | 300 | 200.00 |
| 1,650 | 300 | 181.82 |
| 1,800 | 300 | 166.67 |
Common questions
Is a higher or lower ratio better?
Higher hp/t or kW/t means more power per unit mass. Lower lb/hp or kg/kW means less mass for each unit of power. These express the same direction of change using reciprocal conventions; always read the units before comparing numbers.
Are hp and PS interchangeable?
No. Metric horsepower (PS) and mechanical horsepower use different definitions. Select the unit in the specification. For example, 300 PS is about 295.90 mechanical hp, so treating PS as hp would overstate the hp-based ratio.
Does tonne mean a U.S. ton?
No. Every per-tonne result here uses 1,000 kg. A U.S. short ton is 2,000 lb and is a different mass. Do not compare hp per short ton directly with this tool's hp/t result.
Should I use crankshaft or wheel horsepower?
The calculator can divide either by mass, but it does not convert between them. Label the basis in your own records and compare like with like. There is no automatic drivetrain-loss correction.
Should driver and fuel be included?
Include them when comparing the vehicle as operated. A published curb, dry or test mass may describe a different loading condition. For a specific comparison, document what each mass includes instead of assuming the labels match.
Why is zero power rejected?
The inverse ratios divide by power. At zero power, lb/hp and kg/kW are undefined, so the tool requires a positive value. Positive mass is also needed for the power-per-mass outputs.
How much power matches another ratio?
Multiply the target hp/t by your mass in metric tonnes. For a target of 200 hp/t at 1,650 kg, the required arithmetic value is 200 × 1.65 = 330 mechanical hp. This matches a ratio, not a guaranteed performance result.
Sources & calculation method
NIST Guide to the SI, Appendix B.9 distinguishes mechanical and metric horsepower and lists mass conversion factors. This tool applies those unit definitions to the arithmetic ratio of entered power and mass. Internally, mechanical hp uses 550 foot-pound-force per second and PS uses 75 kilogram-force meters per second, with standard gravity 9.80665 m/s². It is not an empirical racing model.
Use the Horsepower and Torque Calculator if you need power from torque at a known RPM. The Aerodynamic Drag Calculator illustrates a separate road-load component that a power-to-weight ratio alone omits.
Reference accessed September 20, 2026. Examples are hypothetical; sources do not endorse this site or provide an independent professional review.
Formula examples and input validation have automated checks. This page has not received an independent automotive professional review. Read our review standards.