Vehicle · Tires
Tire size converter, metric to inches.
Metric to flat-float inches and back, with sidewall height and overall diameter.
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How do you convert a metric tire size to inches?
A metric size such as 265/70R17 gives the section width in millimetres (265), the aspect ratio as a percentage of that width (70), and the rim diameter in inches (17). The sidewall is 265 x 0.70 = 185.5 mm, so the overall diameter is 17 x 25.4 + 2 x 185.5 = 802.8 mm, or 31.6 inches. The width is 265 / 25.4 = 10.4 inches, giving the inch label 31.6x10.4R17. An inch is exactly 25.4 mm.
Going from inches to metric, the sidewall is (diameter - rim) / 2 and the aspect ratio is the sidewall divided by the section width. A 33x12.50R15 has a 9 inch sidewall and 317.5 mm width, an aspect ratio of 72, so the nearest standard metric size is 320/70R15 with a diameter within a fraction of an inch. Real tires are measured on a specified rim, so the published overall diameter can differ from the arithmetic by a little. The result is an equivalent, not an official size listing.
Frequently asked questions
What is 265/70R17 in inches?
About 31.6 inches tall and 10.4 inches wide, written 31.6x10.4R17. The sidewall is 7.3 inches.
What is 33x12.50R15 in metric?
The width is 317.5 mm and the aspect ratio is 72. The nearest standard metric size is 320/70R15, which is a slightly shorter tire.
Are metric and inch sizes exactly equal?
No. The arithmetic gives the nominal dimensions. A real tire's measured diameter depends on the make, the measuring rim and wear.
What does R mean?
R stands for radial construction. The number after it is the rim diameter in inches.
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Scope
Nominal size arithmetic. It is not a fitment guarantee. Confirm tire and wheel sizes with the tire maker or a qualified shop.