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Tire Size Converter: Metric to Inches
Turn any metric tire size, like 275/55R20, into overall diameter, width and sidewall height in inches and millimetres. For drivers who see a size on a tire and want to know how big it really is.
Example: 275/55R20. Also accepts 275/55-20 or 275 55 20.
| Measure | Inches | Millimetres |
|---|---|---|
| Overall diameter | 31.9 in | 810 mm |
| Section width | 10.8 in | 275 mm |
| Sidewall height | 6.0 in | 151 mm |
| Circumference | 100.2 in | 2546 mm |
| Rim diameter | 20 in | 508 mm |
| Revolutions per mile | 632 | |
| Revolutions per km | 393 |
Nominal size from the size code; real tires vary by brand, rim width and inflation. Fit on your vehicle is not checked.
How the conversion works
- Sidewall height (mm) = section width × aspect ratio ÷ 100.
- Overall diameter (in) = rim diameter + 2 × sidewall height ÷ 25.4.
- Circumference = overall diameter × pi, and revolutions per mile = 63,360 ÷ circumference in inches.
For 275/55R20 that is a sidewall of 151 mm, an overall diameter of 31.9 in, a circumference of 100.2 in and 632 revolutions per mile.
The result is the nominal size from the code. Different brands and models of the same size can differ a little, and a tire grows slightly when it is inflated and under load, so treat it as a close estimate.
Common tire sizes in inches
Overall diameter and width for common car, SUV and light-truck sizes, sorted by diameter. Type any of them above for the full breakdown.
| Size | Overall diameter | Width | Sidewall |
|---|---|---|---|
| 205/55R16 | 24.9 in (632 mm) | 8.1 in (205 mm) | 4.4 in |
| 225/45R17 | 25.0 in (634 mm) | 8.9 in (225 mm) | 4.0 in |
| 195/65R15 | 25.0 in (635 mm) | 7.7 in (195 mm) | 5.0 in |
| 245/40R18 | 25.7 in (653 mm) | 9.6 in (245 mm) | 3.9 in |
| 225/50R17 | 25.9 in (657 mm) | 8.9 in (225 mm) | 4.4 in |
| 215/60R16 | 26.2 in (664 mm) | 8.5 in (215 mm) | 5.1 in |
| 215/55R17 | 26.3 in (668 mm) | 8.5 in (215 mm) | 4.7 in |
| 235/45R18 | 26.3 in (669 mm) | 9.3 in (235 mm) | 4.2 in |
| 205/65R16 | 26.5 in (673 mm) | 8.1 in (205 mm) | 5.2 in |
| 245/45R18 | 26.7 in (678 mm) | 9.6 in (245 mm) | 4.3 in |
| 225/55R17 | 26.7 in (679 mm) | 8.9 in (225 mm) | 4.9 in |
| 215/65R16 | 27.0 in (686 mm) | 8.5 in (215 mm) | 5.5 in |
| 235/55R17 | 27.2 in (690 mm) | 9.3 in (235 mm) | 5.1 in |
| 225/60R17 | 27.6 in (702 mm) | 8.9 in (225 mm) | 5.3 in |
| 215/70R16 | 27.9 in (707 mm) | 8.5 in (215 mm) | 5.9 in |
| 225/65R17 | 28.5 in (724 mm) | 8.9 in (225 mm) | 5.8 in |
| 235/75R15 | 28.9 in (733 mm) | 9.3 in (235 mm) | 6.9 in |
| 235/70R16 | 29.0 in (735 mm) | 9.3 in (235 mm) | 6.5 in |
| 235/65R17 | 29.0 in (737 mm) | 9.3 in (235 mm) | 6.0 in |
| 255/55R18 | 29.0 in (738 mm) | 10.0 in (255 mm) | 5.5 in |
| 235/60R18 | 29.1 in (739 mm) | 9.3 in (235 mm) | 5.6 in |
| 245/65R17 | 29.5 in (750 mm) | 9.6 in (245 mm) | 6.3 in |
| 245/50R20 | 29.6 in (753 mm) | 9.6 in (245 mm) | 4.8 in |
| 275/60R17 | 30.0 in (762 mm) | 10.8 in (275 mm) | 6.5 in |
| 235/65R18 | 30.0 in (763 mm) | 9.3 in (235 mm) | 6.0 in |
| 255/70R16 | 30.1 in (763 mm) | 10.0 in (255 mm) | 7.0 in |
| 265/50R20 | 30.4 in (773 mm) | 10.4 in (265 mm) | 5.2 in |
| 245/75R16 | 30.5 in (774 mm) | 9.6 in (245 mm) | 7.2 in |
| 245/70R17 | 30.5 in (775 mm) | 9.6 in (245 mm) | 6.8 in |
| 265/60R18 | 30.5 in (775 mm) | 10.4 in (265 mm) | 6.3 in |
| 265/65R17 | 30.6 in (776 mm) | 10.4 in (265 mm) | 6.8 in |
| 265/70R16 | 30.6 in (777 mm) | 10.4 in (265 mm) | 7.3 in |
| 255/55R20 | 31.0 in (789 mm) | 10.0 in (255 mm) | 5.5 in |
| 265/70R17 | 31.6 in (803 mm) | 10.4 in (265 mm) | 7.3 in |
| 265/75R16 | 31.6 in (804 mm) | 10.4 in (265 mm) | 7.8 in |
| 275/55R20 | 31.9 in (810 mm) | 10.8 in (275 mm) | 6.0 in |
| 255/70R18 | 32.1 in (814 mm) | 10.0 in (255 mm) | 7.0 in |
| 255/75R17 | 32.1 in (814 mm) | 10.0 in (255 mm) | 7.5 in |
| 275/65R18 | 32.1 in (815 mm) | 10.8 in (275 mm) | 7.0 in |
| 285/45R22 | 32.1 in (815 mm) | 11.2 in (285 mm) | 5.0 in |
| 285/55R20 | 32.3 in (822 mm) | 11.2 in (285 mm) | 6.2 in |
| 285/65R18 | 32.6 in (828 mm) | 11.2 in (285 mm) | 7.3 in |
| 265/70R18 | 32.6 in (828 mm) | 10.4 in (265 mm) | 7.3 in |
| 285/70R17 | 32.7 in (831 mm) | 11.2 in (285 mm) | 7.9 in |
| 285/75R16 | 32.8 in (834 mm) | 11.2 in (285 mm) | 8.4 in |
| 275/60R20 | 33.0 in (838 mm) | 10.8 in (275 mm) | 6.5 in |
| 275/70R18 | 33.2 in (842 mm) | 10.8 in (275 mm) | 7.6 in |
| 305/55R20 | 33.2 in (844 mm) | 12.0 in (305 mm) | 6.6 in |
| 295/70R17 | 33.3 in (845 mm) | 11.6 in (295 mm) | 8.1 in |
| 285/60R20 | 33.5 in (850 mm) | 11.2 in (285 mm) | 6.7 in |
| 285/70R18 | 33.7 in (856 mm) | 11.2 in (285 mm) | 7.9 in |
| 275/65R20 | 34.1 in (865 mm) | 10.8 in (275 mm) | 7.0 in |
Metric to inches for popular sizes
These sizes are searched for often. Open one for the full breakdown and a list of sizes with nearly the same diameter.
To see how two sizes differ, use the tire size comparison calculator.
Tire size converter FAQ
How do I convert a metric tire size to inches?
Take the first number, the width in millimetres, and multiply it by the aspect ratio (the second number) divided by 100 to get the sidewall height in millimetres. Double it, add the rim diameter converted to millimetres (rim inches times 25.4), then divide the total by 25.4 to get the overall diameter in inches.
What is 275/55R20 in inches?
275/55R20 is about 31.9 inches tall and 10.8 inches wide, on a 20-inch rim.
Why does a 33 inch tire not have a 33 in the size?
Metric sizes give width in millimetres and rim size in inches, so the overall height has to be calculated. Flotation sizes such as 33x12.50R15 state the overall diameter directly. This converter reads metric sizes only.
Is the real tire exactly this size?
No. The figures are calculated from the size code. A real tire varies with brand, model, the rim width it is mounted on, inflation and wear, and can differ by a few tenths of an inch.