Tire section width guide
What does the section width number mean?
The section width (e.g. 205 in 205/55R16) is the widest measurement of the unmounted tire in millimetres, measured from sidewall to sidewall. A wider tire generally provides more grip but increases rolling resistance and may not fit narrower rims or tight wheel arches.
Decode a tire size
Type the main sidewall size string to see the width, profile and sidewall math.
- Section width
- 225 mm
- Aspect ratio
- 45%
- Sidewall height
- 101.3 mm
- Overall diameter
- 634.3 mm
Reference-table value only. Always match your vehicle placard and tire sidewall markings.
Worked examples
Metric and flotation markings look different, but the table is calculated from the same nominal diameter, width and rim-size rules.
| Size | Overall diameter | Section width | Sidewall | Circumference |
|---|---|---|---|---|
| 225/45R17 | 24.97 in / 634 mm | 8.86 in / 225 mm | 3.99 in / 101.3 mm | 78.45 in / 1993 mm |
| 285/75R16 | 32.83 in / 834 mm | 11.22 in / 285 mm | 8.42 in / 213.8 mm | 103.14 in / 2620 mm |
| 33x12.50R15 | 33.00 in / 838 mm | 12.50 in / 318 mm | 9.00 in / 228.6 mm | 103.67 in / 2633 mm |
What to do with it: Round marketing sizes can hide several millimetres of difference.
Tire & wheel reference guides · How to read a tire size · Rim diameter guide
Seasonal check
Winter tire rules coming up?
Check tread depth, markings and local winter requirements before the first cold spell instead of waiting for the appointment rush.