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Tire size calculator

Decode a sidewall code like 225/45R17 into section width, sidewall height, overall diameter, and revolutions per mile. Then compare close equivalents that stay within 3% diameter — same rim first, which is what you want for a wheel already in the yard.

Metric like 225/45R17, or flotation like 31x10.50R15.

225/45R17

24.97" overall diameter

Section width

225 mm · 8.86"

Sidewall height

101.3 mm · 3.99"

Aspect ratio

45%

Rim diameter

17"

Revolutions per mile

808

Close equivalents

Within 3% overall diameter. Same rim size is listed first, which is what you want for a wheel already in the yard.

How to read a tire size

  1. Enter a metric size such as 225/45R17 or a flotation size such as 31x10.50R15.
  2. Read width, sidewall, rim, and overall diameter.
  3. Pick a close equivalent with the same rim if you are matching a wheel you already have.

Frequently asked questions

What does 225/45R17 mean?

225 is the width in millimeters, 45 is the sidewall as a percent of that width, R means radial, and 17 is the rim diameter in inches.

How close should an equivalent tire be?

Stay within about 3% overall diameter so speedometer error and clearance stay reasonable. Same rim diameter matters more than matching width when you are putting a tire on a yard wheel.

Can I decode flotation sizes like 31x10.50R15?

Yes. The first number is overall diameter in inches, then width, then rim. The calculator also lists metric sizes with a similar diameter on the same rim.

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