What is 33x12.50R17 in metric?

The conversion is exact and the answer does not exist

12.50 in of section width is 317.5 mm, and an 8.00 in sidewall on a 12.50 in section is an aspect ratio of 64. So the honest metric description of this tire is 318/64R17. No manufacturer makes it, no retailer stocks it, and no fitment guide lists it — metric truck sizes cluster on widths ending in 5 and on aspect ratios in multiples of five, and 318/64 misses both conventions.

What you can actually buy at this height

255/80R17 stands 33.06 in, six hundredths of an inch over the target, and is the nearest real metric size on a 17-inch wheel. It is also 10.04 in wide against 12.50 — a shortfall of 2.46 in, which is most of the reason the two tires look nothing alike despite matching on height.

Move down the list and the trade reverses. 295/70R17 measures 33.26 in and 11.61 in wide: a quarter-inch taller than needed, but far closer on width. 285/70R17 goes the other way at 32.71 in. Loading the converter with this code ranks the whole set by diameter difference, with the width shortfall stated alongside each.

Why the two notations cannot agree

Imperial flotation sizing states the diameter and lets the aspect ratio fall out of it. Metric sizing states the width and the aspect ratio and lets the diameter fall out. Converting one to the other is arithmetic, but converting it to something purchasable means landing on the small grid of widths and aspect ratios that are genuinely produced — and that grid has no point at 318/64. The notation reference sets out which fields each system fixes and which it derives.

The practical reading

If someone asks for "the metric equivalent of 33x12.50R17", they are usually asking which metric size they can order instead. The answer depends on whether they need the height or the width, because on a 17-inch wheel no single metric size gives both.