Tire size conversion: metric sizes and inches

Divide millimeters by 25.4 to convert to inches. For a metric tire, calculate overall diameter first. Converting only the width does not give the tire's height.

Metric tire size to inches

For 225/45R17, the nominal overall diameter is 634.3 mm, or 24.97 inches. Its section width is 8.86 inches. The rim remains 17 inches: it was already expressed in inches in the original marking.

The reusable diameter formula is (2 × width × aspect ÷ 100 + rim × 25.4) ÷ 25.4. Use millimeters for width and inches for rim. Keep the full-precision value when comparing sizes, then round the displayed answer. See all calculation formulas.

What does 35x12.50R17 mean?

In flotation notation, the first number supplies nominal overall diameter directly: 35 inches. The next is nominal section width: 12.50 inches. R17 identifies radial construction and a 17-inch rim. In metric dimensions that is 889.0 mm overall diameter and 317.5 mm section width.

Enter this notation directly in FitMyTires. The calculator preserves the supplied diameter instead of inferring and rounding an aspect ratio, which could introduce an unnecessary conversion error.

Compare 35x12.50R17 with 315/70R17

Is 315/70R17 exactly the same as a 35-inch tire?

No. Applying the nominal formula to 315/70R17 gives 34.36 inches overall diameter and 12.40 inches width. It differs from the nominal 35 × 12.50 dimensions. A nearby size label is a comparison candidate, not an exact specification or installation equivalent.

Actual product dimensions can differ from the nominal result. Check the exact tire model's diameter, section width, measuring rim, and approved rim-width range. Tire Rack describes nominal calculations and measuring-rim effects. FitMyTires lets you enter published measurements separately and labels them as user supplied.

Which metric sizes are 31, 32, 33, 34, or 35 inches?

The table groups common light-truck and SUV sizes by nominal overall diameter, calculated from the size marking and rounded to the nearest inch. The inch-style size beside each one is the same calculation written as diameter × section width, not a product sold under that label. Every row opens in the calculator, including sizes that do not have their own reference page.

Why a 33-inch tire is rarely 33.0 inches

An inch class is a label, not a measurement. This table puts every size from 32.50 in to 33.49 in into the 33-inch class. Shops and forums may round or group differently, so a 31.6-inch size can be listed as a 31 or a 32. Flotation markings such as 33x12.50R17 are nominal too, and a specific model's published diameter often differs from the number on the sidewall.

Published diameters are measured on a new tire, mounted on its assigned measuring rim and inflated without load. Tread wear, a different rim width, inflation, and vehicle load all change the diameter you would measure on the vehicle, and a loaded tire's rolling radius is shorter than half its free diameter. Toyo Tires defines overall diameter, measuring rim width, and static loaded radius. Compare the exact model's published figures before relying on a class label.

Convert dimensions before comparing fitment requirements

Two sizes with similar diameter can differ in width, construction, load capacity, or permitted wheel width. Conversion does not settle those differences. Keep the original tire marking and the exact model specification when sharing a comparison, and review the speedometer effect separately from clearance.