Size calculator
Pick a tire size to see its real dimensions. Switch to Inch for sizes like 33x12.50R15.
What the numbers mean
A metric size like 265/70R17 gives the section width in millimetres (265), the sidewall height as a percentage of that width (70%), the construction (R for radial) and the wheel diameter in inches (17). Inch sizes like 33x12.50R15 give the overall height, the width and the wheel size directly.
How the diameter is worked out
Overall diameter is the wheel diameter plus two sidewalls. For 265/70R17 that is 17 in plus 2 × 185.5 mm, or about 31.6 in. Circumference and revs per mile follow from the diameter. A real tire usually measures a little under its nominal size, and the exact figure depends on the brand, the tread depth and the wheel width.