What is Tyre Size Calculator?
Tyre Size Calculator helps you compare tyre dimensions, overall diameter and geometric size changes.
The main result is overall tyre diameter, with a breakdown of sidewall height, rolling circumference and revolutions per km. The formula, example and assumptions below explain how to interpret it.
How to use Tyre Size Calculator
Use the example to get familiar with the form, then enter your own figures. Any rates in the example are illustrative. Check the field labels and units before calculating.
- Gather tyre section width (mm), sidewall aspect ratio (%) and rim diameter (inches). Use values from the same situation or reporting period.
- Replace the example tyre section width with your own value, then complete the other fields. Check the displayed units.
- Select Calculate and read overall tyre diameter with its result breakdown. Change one input and calculate again to compare a second scenario. Reset restores the original example.
- Enter tyre section width in mm, at least 1 and at most 1000. Decimals are accepted.
- Enter sidewall aspect ratio in %, at least 0 and at most 100. Decimals are accepted.
- Enter rim diameter in inches, at least 1 and at most 100. Decimals are accepted.
Tyre Size Calculator: a worked example
With the inputs below, the result is 631.9 mm (overall tyre diameter). Follow the example, then replace these illustrative values with your own.
| Input or output | Example value |
|---|---|
| Tyre section width (mm) | 205 mm |
| Sidewall aspect ratio (%) | 55 % |
| Rim diameter (inches) | 16 inches |
| Overall tyre diameter | 631.9 mm |
| Sidewall height | 112.75 mm |
| Rolling circumference | 1,985.172398 mm |
| Revolutions per km | 503.734588 |
Understanding the Tyre Size result
Read overall tyre diameter alongside sidewall height, rolling circumference and revolutions per km. These describe different parts of the same calculation.
Displayed results use a readable number of decimal places. When checking a result by hand, keep extra precision until the last step. To compare scenarios, change one input at a time and keep the others fixed.
- Example Sidewall height: 112.75 mm
- Example Rolling circumference: 1,985.172398 mm
- Example Revolutions per km: 503.734588
Tyre Size Calculator: assumptions and common mistakes
A useful estimate starts with the right inputs. Check the following assumptions and limits before applying the result to your situation.
- Use mileage from comparable driving conditions. A fuel-only comparison excludes financing, maintenance and resale unless those amounts are specifically entered.
For wider guidance, visit Bureau of Energy Efficiency. The formula and scope of this specific tool are stated on this page.
