Axle ratio (also called differential or final drive ratio) is how many times the driveshaft rotates for every one full rotation of the axle. A 4.10 ratio means the driveshaft spins 4.1 times per wheel revolution, multiplying torque 4.1x.

How do I count ring and pinion teeth?

Remove the differential cover, rotate the pinion and count how many times the ring gear rotates per one full pinion rotation, or physically count the teeth on each gear. Mark a tooth as a starting point and count each one around the gear circumference.

Is a higher or lower axle ratio better?

Higher numeric ratios (e.g. 4.56) produce more torque multiplication for better acceleration and towing, but increase engine RPM at highway speeds, hurting fuel economy. Lower ratios (e.g. 2.73) cruise at lower RPM but sacrifice pulling power.

How does tire size affect effective axle ratio?

Larger tires act like a numerically lower gear ratio because each revolution covers more ground. Fitting 35-inch tires on a truck geared for 31-inch tires effectively lowers the ratio, reducing off-the-line torque. Re-gearing restores the factory ratio feel.

What is the RPM formula used here?

Engine RPM = (Vehicle Speed × Transmission Ratio × Axle Ratio × 336) ÷ Tire Diameter (inches). The constant 336 converts mph and inches to RPM for a standard differential.

Axle Ratio Calculator

Enter ring gear and pinion gear tooth counts to instantly calculate your axle ratio and see its effect on engine RPM, vehicle speed, and torque multiplication.

Gear Tooth Counts

Ring Gear Teeth

Large gear inside the differential housing

Pinion Gear Teeth

Small input gear connected to the driveshaft

Optional — RPM at Speed

Tire Diameter (inches)

Transmission Gear Ratio

Use 1.00 for direct drive / top gear

Vehicle Speed (mph)

Enter ring and pinion teeth counts, then click Calculate.

Summary

The Axle Ratio Calculator determines the differential (axle) gear ratio by dividing the number of ring gear teeth by the number of pinion gear teeth. A numerically higher ratio (e.g. 4.10) delivers more torque multiplication and better acceleration, while a lower ratio (e.g. 2.73) favors fuel economy and highway cruising. Use the RPM and speed fields to preview how a ratio change affects engine operating range.

How it works

Enter the number of teeth on the ring gear (the large gear in the differential).
Enter the number of teeth on the pinion gear (the small input gear).
The calculator divides ring teeth by pinion teeth to produce the axle ratio.
Optionally enter tire diameter, transmission gear ratio, and vehicle speed to see required engine RPM.
Review the torque multiplication factor and RPM results to compare ratio options.

Use cases

Verify the ratio of a used axle before swapping it into your vehicle.
Compare a 3.73 vs 4.10 ratio for towing vs. daily driving trade-offs.
Calculate engine RPM at highway speed after a gear swap.
Estimate torque gain when re-gearing for larger tires.
Confirm ring-and-pinion count after purchasing a new gear set.
Plan a re-gear to maintain factory RPM after a tire size change.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu