Tire Comparison Calculator

Enter the sizes of two tires to calculate the diameter, circumference, sidewall, width, and revolutions per mile of each for a side by side comparison. Plus, see the amount of speedometer error for the new tire.

Tire One
/ R
Tire Two
/ R

Tire Comparison:

Tire OneTire TwoDifference

Speedometer Error

SpeedometerActual Speed
30 mph
40 mph
50 mph
60 mph
70 mph
80 mph
90 mph
Note: Revolutions per mile will vary, usually by around 3% when under the load of the vehicle
Learn how we calculated this below

On this page:

How to Compare Tire Measurements

When replacing the tires on your vehicle to a new size it is important to compare the measurements of each of them to help determine if the new tires will work.

The tire comparison calculator will generate all the dimensions of each tire in both inches and millimeters. It will also calculate the difference in each dimension between the tires to allow you to compare and see if the new tire will work for your vehicle.

To learn more about how to find the dimensions of a tire, try our tire size calculator which also shows all the formulas to calculate each dimension.

Icon of a wheel with tire and rim

The comparison calculator will also estimate the amount of speedometer error that will need to be accounted for when upgrading tires on a vehicle. See the error for various speeds in miles per hour or kilometers per hour.

What do the Numbers in a Tire Size Mean?

When entering the size of the old and new tires there are three required values, and they usually take the form like this: 245/40R18.

The section width is the first value before the slash (/), and it’s usually measured in millimeters. This is the width of the tire.

The aspect ratio is the second value after the slash. This is the ratio between the width of the tire and the height of the sidewall.

The rim diameter is the final value after the R. This is the size of the wheel rim and inside diameter of the tire.

When changing the rims on a vehicle it’s also important to ensure the inner clearance and outer position of the new wheel will work with the fender and wheel-well. Try our wheel offset calculator to find the change in inner clearance and outer position of the new wheel.