🚗 Automotive
Gear Ratio Calculator
Engine speed, the gearbox ratio and the final drive ratio together set how fast the wheels turn; tyre diameter then converts that into road speed. This is why fitting larger tyres makes the speedometer under-read: the engine is doing the same work, but each wheel revolution now covers more ground.
How it works
Engine speed
Gear ratio
Final drive ratio
Tyre diameter
Overall ratio
Wheel speed
Road speed
Road speed
Speed per 1000 rpm
Frequently asked questions
How do I use the Gear Ratio Calculator?
Fill in the fields above — the result recalculates instantly as you type. Everything runs in your browser, so the values you enter are never collected or stored.
Is this calculator free?
Yes. It is completely free, requires no account, and works on phones, tablets and desktops.