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About this tool
Convert power and kerb weight into PS/tonne, kW/tonne and kg per PS, plus a physics-based 0-100 km/h estimate.
Power-to-weight ratio is peak power divided by the mass being moved, and it predicts acceleration far better than power alone. This calculator reports the ratio in PS per tonne, kW per tonne, bhp per tonne, watts per kilogram and kilograms carried per PS, using both kerb weight and kerb weight plus rider or passengers. It also estimates 0-to-target-speed time from the work-energy relation t = ½mv² ÷ (k × P), floored by the traction limit t = v ÷ (a × g), so an over-powered machine is correctly reported as wheelie-limited rather than impossibly quick.
Open Power to Weight Ratio Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
PS/tonne, kW/tonne, bhp/tonne, W/kg and kg/PS from a single entry.
Adding the rider changes the number a lot on light vehicles — the calculator shows both.
Flags when acceleration is capped by traction rather than by power.
Around 90-105 PS per tonne is normal for a 125 cc commuter or a 350 cc classic, roughly 150-160 for a 200 cc streetfighter, about 260 for a 390 cc naked and close to 1,000 PS per tonne for a litre-class superbike. Above roughly 400 PS per tonne, acceleration from rest is limited by the front wheel lifting, not by power.
Divide peak power by mass, then scale to the unit you want: PS per tonne = power in PS ÷ (mass in kg ÷ 1000). A 43.5 PS bike weighing 167 kg gives 43.5 ÷ 0.167 ≈ 260 PS per tonne at kerb weight, dropping to about 180 with a 75 kg rider aboard.
Yes, if you want a figure that reflects real acceleration. A 75 kg rider adds nearly 45% to a 167 kg motorcycle's mass, so the laden ratio is the honest one; manufacturers quote the kerb figure because it looks better.
The estimate uses average delivered power and ignores aerodynamic drag, gearing and tyre temperature, so it typically lands within about 10% of a tested figure. Drag matters most above roughly 120 km/h, and a launch-control start or a cold tyre can move a real result by a second either way.
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