Tire Calculator
Type a tire size and instantly see its diameter, width and sidewall.
Enter size
/R
Width (mm)
Aspect %
Rim (in)
Results
Diameter
621.5
Section width
185
Sidewall
120.25
Circum.
1952
Revs/km
512
Tire Size Comparison
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Alternative
What do the calculator’s numbers mean?
- Diameter
- The tire’s full height, from the ground to the top of the tread. It decides how far the car travels with each wheel turn, so it is the number to keep close when you change size.
- Section width
- The tire’s width at its widest point. It is the first number of the size, in millimetres.
- Sidewall
- The height of the rubber between the rim and the tread: the width multiplied by the second number of the size, divided by 100.
- Circum.
- The distance the tire rolls in one full turn.
- Revs/km
- How many turns the tire makes in one kilometre. The speedometer counts wheel turns, so a size with a different figure changes the speedometer reading.
How to read a size like 205/55R16
205 is the width in millimetres. 55 is the sidewall height as a percentage of that width: 55% of 205 mm is about 113 mm. R means a radial tire, and 16 is the rim diameter in inches, so this tire fits only a 16-inch wheel. The number and letter that follow the size on the tire, such as 91V, are the load index and the speed rating.
Changing to a different size?
Keep the new size’s overall diameter within 3% of the original, so the speedometer, the odometer and the car’s safety systems stay accurate.
See the sizes inside that window