How to use it
- Type a flotation size (31x10.50R15, 33x12.50R17, 35x12.50R20) or a metric one (285/70R17, LT285/75R16).
- The converter shows the overall diameter and width in inches and millimeters.
- Below, it lists the closest metric sizes for each common rim diameter, with the difference in percent.
- Open any match in the comparison to see both tires drawn together and the speedometer change.
How flotation sizes work
Flotation sizes, common on pickups and off-road vehicles in the US and Mexico, give the overall diameter, the section width and the rim diameter directly, all in inches. 33x12.50R17 means a tire about 33 in (838.2 mm) tall and 12.50 in (317.5 mm) wide, radial, for a 17 in rim. Metric sizes describe the same tire indirectly, through the width in millimeters and the sidewall as a percentage of it, so the height has to be calculated.
Metric to inches: add both sidewalls (width × aspect ratio ÷ 100 × 2), divide by 25.4 and add the rim. For 285/75R16 that is 427.5 mm, or 16.83 in, plus 16 in of rim: 32.83 in.
33-inch tires in metric
| Rim | Metric size | Diameter | vs 33 in |
|---|---|---|---|
| 15 in | 305/75R15 | 33.01 in (838.5 mm) | +0.04% |
| 16 in | 285/75R16 | 32.83 in (833.9 mm) | −0.51% |
| 17 in | 285/70R17 | 32.71 in (830.8 mm) | −0.88% |
| 17 in | 295/70R17 | 33.26 in (844.8 mm) | +0.79% |
| 18 in | 275/70R18 | 33.16 in (842.2 mm) | +0.48% |
| 20 in | 275/60R20 | 32.99 in (838.0 mm) | −0.02% |
| 20 in | 295/55R20 | 32.78 in (832.5 mm) | −0.68% |
31 and 35 inches
| Nominal height | Metric size | Diameter | Difference |
|---|---|---|---|
| 31 in | 265/75R15 | 30.65 in (778.5 mm) | −1.13% |
| 31 in | 245/75R17 | 31.47 in (799.3 mm) | +1.51% |
| 31 in | 265/70R17 | 31.61 in (802.8 mm) | +1.96% |
| 35 in | 315/75R16 | 34.60 in (878.9 mm) | −1.14% |
| 35 in | 315/70R17 | 34.36 in (872.8 mm) | −1.82% |
| 35 in | 325/60R20 | 35.35 in (898.0 mm) | +1.01% |
Nominal vs real size
The numbers in a tire size are nominal. Real 33 in tires from different brands typically measure about 32.5 to 32.9 in, and mud-terrain treads often stand taller than all-terrain ones of the same size. Width varies too: a 12.50 in tire is 317.5 mm wide on paper, about 1.3 in wider than a 285 mm metric tire. For a tight fit, check the maker's published diameter and width for the exact model.
Same size is not the same tire
The converter finds a tire of similar size, not the same construction. LT (light truck) and many flotation tires are built for higher loads and pressures than P-metric passenger tires. Keep the load index or load range at least as high as the original, and set the pressure for the tire you actually fit.
Questions
What is 33x12.50R17 in metric?
About 838 mm tall and 318 mm wide. On a 17 in rim, the closest metric sizes are 285/70R17 (32.71 in) and 295/70R17 (33.26 in).
Is 285/75R16 a 33-inch tire?
Close. On paper it is 833.9 mm, or 32.83 in, and it is widely sold and fitted as a metric 33.
Why don't inch and metric sizes match exactly?
Metric widths come in 10 mm steps and aspect ratios in steps of 5, so the diameter can only land near a round number of inches. Brands also differ by a few millimeters.
What does the R mean in 33x12.50R17?
Radial construction. The number after it is the rim diameter in inches; LT at the end marks a light truck tire.