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The free automotive toolbox: tires, wheels, mechanical and performance calculators, no account needed.
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 →