A tire size converter does one job: take a stamp and report it in the other language. Metric to inches. Metric to a flotation equivalent. The calculator above is the converter. The tables below are the worked cases people search as tire size conversion.
Metric to inches
Width (in) = mm / 25.4. Sidewall (in) = width (in) × aspect / 100. Diameter (in) = rim + 2 × sidewall. 275/65R20 becomes 10.8 in wide, 7.0 in sidewall, 34.1 in overall. The in inches hub lists the high-volume stamps already done.
Metric to flotation
Flotation prints the diameter first. There is no exact metric twin for a 33x12.50, because 12.50 inches of width is 317.5 mm, and metric widths step by 10 mm. The honest conversion is "nearest diameter, then nearest width," not a single stamp.
| Flotation | Diameter | Nearest metric | Metric diameter |
|---|---|---|---|
| 31x10.50R15 | 31.0 in | 265/75R15 (not in catalog) | 30.6 in typical |
| 33x12.50R17 | 33.0 in | 285/70R17 | 32.7 in |
| 35x12.50R17 | 35.0 in | 315/70R17 | 34.4 in |
| 37x12.50R17 | 37.0 in | 315/75R16 | 34.6 in (not close) |
315/70R17 is not a 35. It is 34.4. People buy it as a "35" because it is the tallest common 17-inch metric that still fits a lot of 17-inch truck wheels. The converter will not flatten that into a marketing label.
The question the converter keeps getting
Is 275/65R20 a 33-inch tire? No. Is 275/60R20? That one is 33.0 inches, so yes, on height. Is 285/70R17 a 33? 32.7 inches, close enough that shops call it a 33. The 33 vs 35 page is this argument with both bands on the table.
Landing on a flotation equivalent does not mean that tire mounts on your wheel or clears the well. It means the diameters are in the same conversation.