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
e.g. 225/65R17 or 28.5x9R17

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

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How to Compare Tires

When changing the tires on your vehicle to a new size, it’s important to compare the measurements and sizes of each of them to help determine if the new tires will work. You need to ensure the new tires will fit the vehicle, look right, and account for speedometer error.

The first step to comparing tires is to calculate the size of each tire, then compare the key dimensions.

The tire comparison calculator above 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.

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.

You can compare P-metric, euro metric, LT, and flotation tire sizes.

What do the Numbers in a Tire Size Mean?

When entering the size of the old and new tires, there are three required values from the metric tire size. A tire size usually looks something like this: 245/40R18.

graphic showing how to read and calculate a tire size and what the parts of a p-metric size are

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

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.