Two ways to write a tire size
Metric sizes, like 265/70R17, give the section width in millimetres (265), the aspect ratio (70, the sidewall is 70% of the width) and the rim diameter in inches (17). Flotation or inch sizes, common on off-road and light truck tires, give the overall height first: 33x12.50R15 is 33 in tall, 12.50 in wide, on a 15 in rim. This converter reads either kind and works out which one you typed.
Metric to inches
The width converts directly, and the height comes from the sidewall:
width (in) = width (mm) ÷ 25.4
diameter (in) = rim + 2 × width (mm) × aspect ÷ 100 ÷ 25.4Worked example, 265/70R17: the width is 265 ÷ 25.4 = 10.43 in. The sidewall is 265 × 0.70 = 185.5 mm, or 7.30 in, so the diameter is 17 + 2 × 7.30 = 31.61 in (802.8 mm). Written as an inch size, that is 31.6x10.4R17. This is also how to use the page as a tire height or tire diameter calculator: the height of a tire is its overall diameter.
Inches to metric
An inch size rarely has an exact metric twin, so the converter searches every metric width from 125 to 405 mm and every aspect ratio from 25 to 85 on the same rim, and ranks them by how close they come. Height counts four times as much as width in the ranking, because height is what changes your speedometer and clearance.
score = |diameter difference| + 0.25 × |width difference|Worked example, 33x12.50R15: the closest metric size is 305/75R15 at 33.01 in, just 0.01 in taller and 0.49 in narrower. Next come 325/70R15 (32.91 in) and 285/80R15 (32.95 in). For 35x12.50R17 the same search gives 305/75R17 at 35.01 in.
What the numbers do not tell you
Flotation sizes are nominal: a tire sold as 33 in tall often measures a little less once mounted. Metric sizes vary by maker and model too. The matches here are computed from the size codes, so check that the size you pick is made in the construction and load range you need, and compare the maker's published dimensions. Whether it fits your vehicle depends on your wheels and suspension, so check clearance before you buy.
Questions
What is 265/70R17 in inches?
About 31.6 inches tall and 10.4 inches wide: 31.6x10.4R17. The sidewall is 185.5 mm (7.30 in) and the overall diameter 31.61 in.
What metric size is a 33x12.50R15?
The closest by the formula is 305/75R15 at 33.01 in tall and 12.01 in wide. 325/70R15 (32.91 in) and 285/80R15 (32.95 in) are also close.
What metric size equals a 35 inch tire on a 17 inch rim?
305/75R17 works out to 35.01 in, and 325/70R17 to 34.91 in. Check which sizes are made in the tire you want.
How do I calculate tire height?
Multiply the width in mm by the aspect ratio, divide by 100 and by 25.4 to get the sidewall in inches, double it and add the rim. For 285/75R16: 16 + 2 × 8.42 = 32.83 in.