Power-to-Weight Calculator Widget
Rank cars, bikes and trucks by the figure that best predicts acceleration. Enter power in hp, PS or kW and weight in kg or lb and get kW per tonne, horsepower per tonne or per US ton, and kilograms or pounds per horsepower - then compare a second vehicle on the same scale.
Live preview
Under the widget on your page: Powered by A2Z Tools
Embed code
<iframe src="https://a2z.tools/embed/w/power-to-weight-calculator" title="Power-to-Weight Calculator by A2Z Tools" width="100%" height="680" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>
A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.
<div data-a2z-widget="power-to-weight-calculator" data-height="680"></div> <script async src="https://a2z.tools/embed.js"></script>
Adds a small script (what it does) that sizes the widget to fit its content, loads it lazily and keeps it isolated from your page's CSS.
Works with
How it works
Power is first converted to watts with the NIST factors: one mechanical horsepower (550 foot-pounds-force per second, the SAE hp) is 745.6999 W and one metric horsepower (PS, CV, ch) is 735.4988 W, so 100 PS is 98.6 hp. Weight is converted to kilograms with 1 lb = 0.45359237 kg. The widget then reports kilowatts per metric tonne (1,000 kg), horsepower per tonne and per US short ton (2,000 lb), and the inverse figures, kilograms and pounds per horsepower, where smaller means quicker. Metric publishers see kW/t first, imperial ones lb/hp. A 150 kW car weighing 1,500 kg has exactly 100 kW/t, or 7.46 kg per hp. Turn on the comparison to enter a second vehicle in the same units; the widget shows its ratio and how much more power per tonne the stronger one has. Zero or negative inputs are refused.
Calculation method
- Watts = hp x 745.6999, PS x 735.4988 or kW x 1000
- kg = lb x 0.45359237
- kW per tonne = kW / (kg / 1000); hp per tonne = hp / (kg / 1000)
- hp per US ton = hp / (lb / 2000)
- kg per hp = kg / hp; lb per hp = lb / hp
Worked examples
Metric hot hatch
Inputs: 150 kW; 1,500 kg
Result: 100 kW per tonne; 134.1 hp per tonne; 7.46 kg per hp
150 kW = 201.2 hp = 203.9 PS.
US muscle car
Inputs: 300 hp; 3,300 lb
Result: 11 lb per hp; 181.8 hp per US ton; 149.5 kW per tonne
3,300 lb = 1.65 short tons.
Limitations
- Uses peak power; the power available across the rev range and gearing are not considered.
- Manufacturer power and weight figures are measured under different standards and conditions.
Where publishers use it
- A car review site's spec comparison table
- A motorsport club's class rules page that limits kW per tonne
- A motorcycle forum comparing sports bikes
- A truck and trailer guide explaining minimum power for hauling
- A physics teacher's lesson on power, mass and acceleration
Questions
What is the difference between hp, PS and kW?
kW is the SI unit. Mechanical horsepower (hp, as used by SAE in the US) is 745.6999 W; metric horsepower (PS in Germany, CV in Italy and France) is 735.4988 W, about 1.4% smaller. So a 300 PS engine is 220.6 kW or 295.9 hp.
Which weight should I use?
Kerb weight from the manufacturer is the usual basis. Adding a 75 kg driver gives a more realistic figure, especially for light cars and motorbikes where the rider is a large share of the total.
Is higher or lower better?
For kW/t and hp/t, higher is quicker. For kg/hp and lb/hp, lower is quicker - a car at 5 kg/hp has twice the power for its weight of one at 10 kg/hp.
Why do two cars with the same ratio accelerate differently?
Gearing, traction, launch control, torque curve and aerodynamic drag all matter. Power-to-weight is a good first predictor of in-gear acceleration, much less so of 0-60 times from a standstill.
What is a US ton versus a tonne?
A US short ton is 2,000 lb (907.18 kg); a metric tonne is 1,000 kg. 181.8 hp per US ton is about 200.4 hp per tonne.
Sources
- NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity - National Institute of Standards and Technology . Horsepower (550 ft·lbf/s) = 745.6999 W; horsepower (metric) = 735.4988 W; pound (avoirdupois) = 0.4535924 kg. Checked 2026-10-01.
Cite or recommend this tool
If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.
A2Z Tools Power-to-Weight Calculator https://a2z.tools/embed/power-to-weight-calculator
<a href="https://a2z.tools/embed/power-to-weight-calculator">A2Z Tools Power-to-Weight Calculator</a>
[A2Z Tools Power-to-Weight Calculator](https://a2z.tools/embed/power-to-weight-calculator)
Power-to-Weight Calculator by A2Z Tools - https://a2z.tools/embed/power-to-weight-calculator
Related widgets
-
Overall ratio, output rpm and output torque for one to three meshing gear pairs from tooth counts.
-
Length, mass, volume, area, temperature, speed, time, data, pressure, energy and power - exact factors.
-
Road speed from engine rpm, gear, final drive and tyre size - or the rpm needed for a given speed.
-
Fuel needed and trip cost from distance, economy and fuel price, split between passengers.
-
Convert between MPG (US), MPG (UK), L/100 km and km per litre with exact factors.
-
Monthly car payment with down payment, trade-in, sales tax and fees, plus the total cost.