ElpiAutoTire Size Converter
Metric ↔ inch, both ways. 235/75R15 and 28.9×9.3R15 are the same tire.
Your tire size
e.g. 235/75R15, 33X12.50R15, or 225/45R17 91V
Why two numbers
Metric and inch tire sizes
A metric tire size like 235/75R15 is millimetre-based: 235 mm section width, a sidewall 75% of that, on a 15-inch wheel. Most road cars use it. An inch (or “flotation”) size like 33X12.50R15 states overall height, width and wheel directly in inches — common on trucks and off-road tires. They describe the same tires; a shop may list one and a forum the other. This metric tire calculator translates between them and spells out the raw dimensions.
Tire size conversion chart
Common metric sizes and their inch / flotation equivalents, by wheel diameter. Figures are geometric estimates — real tires vary by brand by 1–3%.
Metric equivalents by tire height
Shopping by overall diameter — “I want 35s” — here is the closest metric size on each common wheel. Within about ±0.4″ of the target.
Popular tire size conversions
The conversions people look up most. Click any size to open it in the converter.
| Size | Converts to | Diameter |
|---|---|---|
| 205/55R16metric | ≈ 24.9x8.1R16 | 24.9″ |
| 225/45R17metric | ≈ 25x8.9R17 | 25.0″ |
| 225/55R16metric | ≈ 25.7x8.9R16 | 25.7″ |
| 235/45R17metric | ≈ 25.3x9.3R17 | 25.3″ |
| 245/45R18metric | ≈ 26.7x9.6R18 | 26.7″ |
| 245/40R18metric | ≈ 25.7x9.6R18 | 25.7″ |
| 255/55R18metric | ≈ 29x10R18 | 29.0″ |
| 275/65R18metric | ≈ 32.1x10.8R18 | 32.1″ |
| 265/70R17metric | ≈ 31.6x10.4R17 | 31.6″ |
| 285/70R17metric | ≈ 32.7x11.2R17 | 32.7″ |
| 265/75R16metric | ≈ 31.6x10.4R16 | 31.6″ |
| 245/75R16metric | ≈ 30.5x9.6R16 | 30.5″ |
| 285/75R16metric | ≈ 32.8x11.2R16 | 32.8″ |
| 295/70R17metric | ≈ 33.3x11.6R17 | 33.3″ |
| 315/70R17metric | ≈ 34.4x12.4R17 | 34.4″ |
| 31X10.50R15inch | ≈ 265/75R15 | 31.0″ |
| 33X12.50R15inch | ≈ 320/70R15 | 33.0″ |
| 35X12.50R17inch | ≈ 320/70R17 | 35.0″ |
| 275/55R20metric | ≈ 31.9x10.8R20 | 31.9″ |
| 305/55R20metric | ≈ 33.2x12R20 | 33.2″ |
Tire size pages
The math
How the conversion works
Everything comes off the 25.4 mm in one inch. Take 235/75R15, step by step:
- Section width to inches. 235 mm ÷ 25.4 = 9.25 in.
- Sidewall height. The 75 is a percentage, not a measurement: 75% of 235 mm = 176.25 mm ÷ 25.4 = 6.94 in.
- Overall diameter. Two sidewalls stack on the rim: 15 + 2 × 6.94 = 28.9 in.
- Write it in inches. Height × width on the same wheel:
28.9x9.3R15.
Going the other way, a flotation size like 33X12.50R15 already states diameter, width and wheel in inches — the metric equivalent is the standard width and aspect ratio that reproduce the same overall diameter.
To compare two sizes side by side, use the tire size comparison; to decode one size and see the alternatives that fit its wheel, the tire size calculator.
Common questions
How do I convert a metric tire size to inches?
Overall diameter in inches = wheel diameter + 2 × (section width in mm × aspect ratio ÷ 100) ÷ 25.4. For the metric tire 235/75R15 that is 15 + 2 × (235 × 75 ÷ 100) ÷ 25.4 ≈ 28.9 in. Section width in inches is the millimetre figure ÷ 25.4, so 235 mm ≈ 9.25 in. That makes 235/75R15 roughly a 28.9×9.3R15 in inch/flotation notation. This metric tire calculator does it for any size in either direction.
What is 33 inch tire in metric?
There is no single metric equivalent — several metric sizes land near 33 in tall depending on width and wheel. On a 17-inch wheel, 285/75R17 (≈ 33.8 in) and 265/70R17 (≈ 31.6 in) bracket it; 285/70R17 is about 32.7 in. Enter a target above and the tool shows the closest metric size for a given wheel.
Is the conversion exact?
No. Both notations are nominal. A metric-to-inch conversion is geometry from the code; the moulded tire varies by brand by roughly 1–3%. Flotation sizes are rounded to the nearest half-inch by most makers. Treat the converted number as ±3%.
What does the second number in a metric size mean?
It is the aspect ratio — the sidewall height as a percentage of the section width, not a measurement in its own right. 235/75R15 has a sidewall that is 75% of 235 mm = 176 mm ≈ 6.9 in. A lower number is a shorter, stiffer sidewall.
Metric vs flotation — which is bigger?
Neither notation is inherently bigger; they describe the same tires. 285/70R17 and 33X11.50R17 are within a few tenths of an inch of each other. Off-road sizes are usually quoted in flotation (inches), road-car sizes in metric.
Methodology
Metric sizes are converted with the standard geometric model: overall diameter = wheel diameter + two sidewalls, sidewall = section width (mm) × aspect ratio ÷ 100, all divided by 25.4 for inches. Circumference is π × diameter. Flotation sizes are read as their stated dimensions; their metric equivalent is the standard section width and aspect ratio that reproduce the same overall diameter, rounded to the nearest 5. Actual moulded tires vary by brand by roughly 1–3%.
Reviewed 2026-09-11.