Tire size converter
Turn a metric size like 265/70R17 into inches, convert an inch size like 33×12.50R15 to metric, and compare two sizes side by side.
Diameter difference
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- Speedometer reads 60, you are going
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- Inch size as metric
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Reading a tire size
In 265/70R17, 265 is the section width in millimeters, 70 means the sidewall is 70% as tall as the tire is wide, and 17 is the wheel diameter in inches. There are two sidewalls, so the sidewall height counts twice.
Inch sizes like 33×12.50R15 list the overall diameter, the section width and the wheel. The converter works out the equivalent metric width and aspect ratio. For the new size's effect on rpm and regearing, use the gear ratio, rpm & speedometer calculator.
Frequently asked questions
How do I read a metric tire size like 265/70R17?
265 is the tread width in millimeters, 70 is the aspect ratio (sidewall height as a percentage of that width), R means radial construction, and 17 is the wheel diameter in inches — this calculator converts that whole size into an overall diameter and other inch-based figures.
Can I compare a metric size and an inch size directly?
Yes — that's exactly what the side-by-side comparison is for, converting both into the same units (typically overall diameter in inches) so you can see how a metric-sized tire actually compares to a traditional inch-sized one like 33x12.50R15.
Why does a small aspect ratio change matter so much?
Aspect ratio is a percentage of the tread width, so on a wide tire even a modest-looking percentage change in aspect ratio translates into a real difference in actual sidewall height and therefore overall tire diameter.
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