Power to weight ratio calculator
Specific power in kW per tonne, hp per tonne and kg per hp.
Fill in the fields and the result will appear here automatically.
Compares power with the vehicle’s calculated mass, including a separately entered payload. PS means metric horsepower, 735.49875 W; kW means kilowatts. Mechanical hp is a different unit, so check the unit in the data source before comparing. kW/t and the inverse kg/PS describe a ratio, not a guaranteed acceleration time or vehicle class.
How it works
Formula and logic
Power is converted to kilowatts, mass to tonnes, and the ratio follows; kg per hp is the same relationship inverted. Calculated mass = entered mass + payload. Power and base mass are positive, payload is nonnegative, and the power unit is explicitly selected. Additional output rows must also be numerically representable. Do not add people or fuel twice if already included in the base mass.
Example
150 metric PS in a 1400 kg car is 110.32 kW over 1.4 t, which is 78.80 kW per tonne.
Fields and units
- Engine power — PS / kW
- Power unit — list option
- Kerb weight, kg — kg
- Extra load, kg — kg
How to use
- — Enter engine power and pick its unit.
- — Enter the kerb weight.
- — Add any extra load you want included.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- NIST SP 811 B8: units and metric PS versus mechanical hp; tabulated factors are rounded
- Limitation
- Calculated mass = entered mass + payload. Do not add people or fuel twice if already included in the base mass.
FAQ
Which horsepower is used?
The PS option uses metric horsepower: 1 PS = 735.49875 W. Mechanical hp is approximately 745.7 W and is not the same input. Convert a source given in mechanical hp to kW or PS first.
Should I include passengers and fuel?
That is your choice. Kerb weight is the usual basis for comparison, and the extra load field lets you add whatever you want counted.
Why show kilograms per horsepower as well?
Many people remember the figure that way, and a lower number means better acceleration, which some find more intuitive.
Does this predict acceleration?
Only roughly. Gearing, traction, aerodynamics and where the power arrives in the rev range all matter and are not modelled.