Two notations
Metric to Inch Tire Conversion
A metric size states width and a percentage; a flotation size states height and width in inches. Neither converts exactly into the other, because they are graduated differently. This gives you the real inch measurements for any metric size, and the nearest point on the other notation's ladder along with exactly how far off it lands.
Type a metric size (285/70R17) to get inches, or a flotation size (33x12.50R17) to get metric.
In inches
32.71″ tall × 11.22″ wide
285/70R17 stands 32 11/16″ tall on a 17″ wheel, with a 7.85″ sidewall and a section width of 285 mm (11.22″).
Nearest size on the flotation ladder
33x11.50R17
Close, but not identical: 33.00″ against 32.71″, a difference of 0.29″ in height and 7 mm in section width.
Landing on the ladder is not the same as being in a catalogue. Check that a manufacturer actually lists this size before ordering.
| Dimension | Metric | Imperial |
|---|---|---|
| Section width | 285.0 mm | 11.22″ |
| Sidewall height | 199.5 mm | 7.85″ |
| Wheel diameter | 431.8 mm | 17.0″ |
| Overall diameter | 830.8 mm | 32.71″ |
| Rolling circumference | 2,610.0 mm | 102.76″ |
| Revolutions per mile | 383.1 / km | 616.6 / mile |
| Measuring rim (estimate) | 216 mm | 8.5″ |
How the two codes differ
The metric code — 285/70R17 — gives section width in millimeters, sidewall as a percentage of that width, and wheel diameter in inches. Overall height is never stated; it has to be derived. The flotation code — 33x12.50R17 — gives overall diameter and section width in inches, with the aspect ratio left implicit.
That is why conversion is lossy in both directions. A flotation height is marked in whole inches — 31, 32, 33, 35, 37 — and its width in one-inch steps that always end in .50: 9.50, 10.50, 11.50, 12.50. A metric size is built from a section width on the production ladder and an aspect ratio in steps of five. The two grids do not line up, so a metric size almost never lands exactly on a flotation one. When someone says a 285/70R17 “is a 33”, they mean it is nearer 33 than 32 — the actual number is 32.71″.
Metric and flotation sizes side by side
Each row pairs a metric size with the nearest point on the flotation grid, computed the same way the calculator above computes it. The differences are the point: the two codes rarely land on the same tire, and landing on the grid does not mean a manufacturer catalogues that exact size.
| Metric size | Height | Width | Nearest inch size | Height | Difference |
|---|---|---|---|---|---|
| 215/75R15 | 27.70″ | 8.46″ | 28x8.50R15 | 28.00″ | 0.30″ / 1 mm |
| 235/75R15 | 28.88″ | 9.25″ | 29x9.50R15 | 29.00″ | 0.12″ / 6 mm |
| 265/75R15 | 30.65″ | 10.43″ | 31x10.50R15 | 31.00″ | 0.35″ / 2 mm |
| 265/70R17 | 31.61″ | 10.43″ | 32x10.50R17 | 32.00″ | 0.39″ / 2 mm |
| 285/70R17 | 32.71″ | 11.22″ | 33x11.50R17 | 33.00″ | 0.29″ / 7 mm |
| 315/70R17 | 34.36″ | 12.40″ | 34x12.50R17 | 34.00″ | 0.36″ / 3 mm |
| 285/75R16 | 32.83″ | 11.22″ | 33x11.50R16 | 33.00″ | 0.17″ / 7 mm |
| 275/65R18 | 32.07″ | 10.83″ | 32x10.50R18 | 32.00″ | 0.07″ / 8 mm |
| 305/60R18 | 32.41″ | 12.01″ | 32x12.50R18 | 32.00″ | 0.41″ / 13 mm |
| 275/60R20 | 32.99″ | 10.83″ | 33x10.50R20 | 33.00″ | 0.01″ / 8 mm |
| 295/55R20 | 32.78″ | 11.61″ | 33x11.50R20 | 33.00″ | 0.22″ / 3 mm |
| 325/60R20 | 35.35″ | 12.80″ | 35x12.50R20 | 35.00″ | 0.35″ / 8 mm |
The final column shows the height difference and the section width difference. On most of these rows the width gap is the larger practical problem.
Common questions about metric to inch conversion
- How do you convert a metric tire size to inches?
- Work out overall diameter in millimeters — wheel × 25.4 plus two sidewalls — then divide by 25.4. For 285/70R17 that is 431.8 + (2 × 199.5) = 830.8 mm, which is 32.71 inches tall. Section width converts directly: 285 ÷ 25.4 = 11.22 inches.
- Is 285/70R17 the same as a 33-inch tire?
- Close, and it is routinely called one. The true figure is 32.71 inches, so it is about a third of an inch under a genuine 33. A 33x12.50R17 is 33.00 inches by definition and 12.50 inches wide against the 285's 11.22, so the flotation tire is meaningfully wider as well as taller.
- Why are some tire sizes in inches and some in millimeters?
- Two standards that never merged. The metric code states section width and a percentage; the flotation code, used mainly for light-truck and off-road tires in North America, states overall diameter and width in inches directly. The wheel diameter is in inches in both.
- Which is bigger, 33x12.50 or 285/70R17?
- The 33x12.50R17 — by 0.29 inches in diameter and 32.5 mm in section width. That width difference is the one that decides whether it rubs, and it is far larger than the height difference people focus on.
To compare any two of these sizes on every dimension at once, use the tire size comparison tool.
Other tire maths on this site
- tire size calculatorRead any tire size code and get overall diameter, sidewall height, circumference and revolutions per mile, with the arithmetic shown.
- tire size comparisonPut two sizes side by side and see the difference in diameter, width, sidewall, ground clearance and speedometer reading.
- tire size chartEvery common size sorted by wheel diameter, with overall diameter in inches and millimeters and revolutions per mile.
- tire diameter calculatorOverall diameter, radius and rolling circumference from the size code, and the reverse — the sizes that produce a diameter you want.
- speedometer error calculatorHow far out your speedometer and odometer read after a tire size change, at any indicated speed.
- plus sizing calculatorLarger wheel, same rolling diameter. Plus one and plus two candidates ranked by how close they hold the original diameter.
- gear ratio calculatorThe axle ratio that restores stock engine rpm after a tire diameter change, plus cruising rpm at any speed.
- rim width rangeThe rim widths a size is designed to mount on, and how section width changes as the rim gets wider.
- tire size meaningWhat every character in 265/70R17 stands for, digit by digit, including the load index and speed rating.