Using the Tire Size Calculator
For a 205/55 R16 marking, enter width 205, aspect ratio 55 and rim diameter 16. The aspect ratio is a percentage of section width, while the rim measurement is in inches. The calculator converts those units before adding the two sidewalls to the rim diameter.
Worked example
Use the example inputs below to reproduce this result. These are the form's starting values, not recommended targets. Changing your inputs updates your result above; this worked example stays fixed for comparison. Results are rounded for display.
Example inputs
- Section width (mm)
- 205
- Aspect ratio (%)
- 55
- Rim diameter (in)
- 16
Example result
- Sidewall height (mm)
- 112.75
- Overall diameter (mm)
- 631.9
- Circumference (mm)
- 1,985.1724
- Revolutions per km
- 503.73459
Method and assumptions
Nominal diameter = rim diameter + twice sidewall height. Actual rolling radius depends on construction, pressure and load.
Use measurements from the same situation
Vehicle and trip estimates are easiest to compare when the inputs refer to the same journey, vehicle or operating condition. Keep the distance unit explicit and separate measured values from planning assumptions. If you change several inputs at once, record which ones changed so that a different result can be traced to a specific assumption.
Common question
Is an aspect ratio of 55 a sidewall height of 55 millimeters?
No. It means the sidewall height is nominally 55% of the section width. A wider tire with the same aspect ratio therefore has a taller nominal sidewall, even though the second number is unchanged.
Guide updated .