Gear Ratio Calculator
Get your axle ratio from ring and pinion tooth counts, then estimate engine RPM at a given speed.
Axle ratio
3.73 : 1
41 ring teeth ÷ 11 pinion teeth = 3.73. The driveshaft turns 3.73 times for each wheel rotation.
Engine RPM (1:1 top gear)
2,908 rpm
Tire RPM
780 rpm
How it works
The axle or final-drive ratio is just the ring gear's tooth count divided by the pinion's. A 41-tooth ring on an 11-tooth pinion gives 3.73:1, meaning the driveshaft spins 3.73 times for every full turn of the wheels.
A numerically higher ratio (say 4.10) multiplies torque for quicker acceleration and towing, but raises cruising RPM and hurts fuel economy. A lower ratio (like 3.08) does the opposite — relaxed, efficient highway cruising with less off-the-line punch.
The optional second step estimates engine RPM at speed. It works out how many times your tire turns per minute at the road speed you enter, then multiplies by the axle ratio, assuming a 1:1 top gear. Bigger tires drop the RPM; a steeper ratio raises it.
Frequently asked questions
What's a good axle ratio for daily driving?
Something in the 3.2 to 3.7 range is a common balance — enough torque to feel responsive without spinning the engine too fast on the highway. Towing and off-road builds often go higher.
Does the RPM figure account for my transmission gear?
It assumes a 1:1 top gear, which most manuals and many autos have in their direct drive. If you're in an overdrive gear (a ratio below 1), your real cruising RPM will be lower than shown.
Why did bigger tires change my RPM and speedo?
A taller tire travels farther per revolution, so it turns fewer times at a given speed. That lowers engine RPM and effectively lowers your gearing, which is why many people re-gear after fitting larger tires.