Tire Size Calculator
Fill in the values and the answer updates as you type.
How the Tire Size Calculator works
Sidewall height = section width × aspect ratio ÷ 100. Overall diameter = 2 × sidewall + rim diameter × 25.4. Keep a new tire within about 3% of the original diameter so the speedometer stays accurate.
Inputs and results
The Tire Size Calculator takes 3 inputs and gives 4 results.
What you enter
- Section width (205 in 205/55R16) (mm) — starts at 205.
- Aspect ratio (55 in 205/55R16) (%) — starts at 55.
- Rim diameter (16 in 205/55R16) (inch) — starts at 16.
What you get
- Overall diameter (mm)
- Sidewall height (mm)
- Circumference (mm)
- Wheel turns per km
Example: Tire Size Calculator with the starting values
With section width (205 in 205/55r16) 205 mm, aspect ratio (55 in 205/55r16) 55 % and rim diameter (16 in 205/55r16) 16 inch, the calculator returns:
| Overall diameter (mm) | 631.9 |
|---|---|
| Sidewall height (mm) | 112.8 |
| Circumference (mm) | 1,985.17 |
| Wheel turns per km | 503.73 |
Change any value above and the results update straight away.
Tire Size Calculator FAQ
How do I use the Tire Size Calculator?
Enter section width (205 in 205/55r16), aspect ratio (55 in 205/55r16) and rim diameter (16 in 205/55r16) in the fields, then read overall diameter (mm), sidewall height (mm), circumference (mm) and wheel turns per km in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Tire Size Calculator calculate?
Overall diameter, sidewall height, and circumference from a tire code. It returns overall diameter (mm), sidewall height (mm), circumference (mm) and wheel turns per km from the 3 values you provide.
What values does the Tire Size Calculator start with?
It opens with section width (205 in 205/55r16) 205 mm, aspect ratio (55 in 205/55r16) 55 % and rim diameter (16 in 205/55r16) 16 inch so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Tire Size Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Tire Size Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.