Tire size conversion chart
Popular metric tire sizes decoded into overall diameter, section width, and revolutions per mile. Use it to compare sizes, check speedometer impact, or find a plus-size that keeps your diameter close.
| Tire size | Overall dia. (in) | Section width (in) | Revs / mile |
|---|---|---|---|
| 195/65R15 | 25.0 | 7.7 | 807 |
| 205/55R16 | 24.9 | 8.1 | 811 |
| 215/60R16 | 26.2 | 8.5 | 770 |
| 225/45R17 | 25.0 | 8.9 | 807 |
| 235/75R15 | 28.9 | 9.3 | 698 |
| 245/75R16 | 30.5 | 9.6 | 661 |
| 265/70R17 | 31.6 | 10.4 | 638 |
| 275/55R20 | 31.9 | 10.8 | 632 |
| 285/75R16 | 32.8 | 11.2 | 615 |
Dimensions are calculated from the size code and are nominal; real mounted dimensions vary by brand, rim width, and inflation. Keep overall diameter within about 3% of stock to avoid speedometer error and clearance problems.
Comparing two specific sizes?
To compare a new size against your current tire and see the speedometer error, use the Tire Size Comparison Calculator, or decode one size with the Tire Size Calculator.
Reading a tire size
A size like 225/45R17 means 225 mm section width, a sidewall 45% of that width, on a 17-inch rim. Overall diameter is the rim plus two sidewalls. The chart does this math so you can compare sizes at a glance.
Staying within 3% diameter
Changing tire size changes your effective gearing and speedometer reading. Keeping the new overall diameter within roughly 3% of stock keeps the speedometer accurate and avoids rubbing. Revs per mile shows how the size affects wheel speed.
FAQ
What does 225/45R17 mean?
225 mm wide, sidewall 45% of the width (about 4.0 in), on a 17-inch wheel, giving roughly a 25-inch overall diameter.
How much bigger tire can I fit?
As a rule of thumb, stay within about 3% of the original overall diameter unless you also correct the speedometer and confirm clearance.
What is revolutions per mile?
How many times the tire turns to cover a mile. A taller tire turns fewer times, which lowers your indicated speed and effective gear ratio.