Free automotive tools
Tires, engine, performance.Every calculation, instantly.
Compare tire sizes, check your speedometer error, convert horsepower to kW or work out engine displacement. Free, no account, on phone or desktop.
8tools
18languages
100 %free
< 1 sinstant results
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The tire size calculator
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All tools, by family
Tires & wheels
Tires & wheelsTire Size CalculatorEnter a tire size (e.g. 225/45R17) to get its diameter, circumference and revolutions per mile or km.Calculate →Tires & wheelsTire Size ComparisonCompare two tire sizes side by side: diameter, ground clearance and speedometer impact.Calculate →Tires & wheelsSpeedometer Error CalculatorAfter a tire size change, find your real speed versus what the speedometer shows.Calculate →Tires & wheelsWheel Offset CalculatorCalculate backspacing, poke and offset (ET) for your wheels.Calculate →
Mechanical & performance
Mechanical & performanceHP to kW ConverterConvert horsepower (HP), metric horsepower (PS) and kilowatts (kW) instantly.Calculate →Mechanical & performanceEngine Displacement CalculatorBore × stroke × cylinder count: get displacement in cc, litres and cubic inches.Calculate →Mechanical & performancePower-to-Weight Ratio CalculatorEnter power and weight to get the ratio in kW/kg and hp per tonne.Calculate →Mechanical & performanceRPM to Speed CalculatorFrom engine RPM, gear ratio, final drive and tire size, calculate theoretical road speed.Calculate →
How it works
Three steps, zero friction.
1
Enter your values
A tire size, a power figure, a bore: only what matters.
2
Read the result
Headline figure, details and diagram, updated instantly.
3
Chain tools
Your values carry over to the next tool, no retyping.