Free Tool
Tractor Tire Size Converter
Tractor tires use several different size formats, and they don't convert with a single multiplier — each format encodes section width, aspect ratio and rim diameter differently. This tool reads a size in any common format and shows what each part of it means, in both inches and millimeters.
Type a size like 710/70R42 (metric radial), 18.4-38 (standard bias), 18.4x38 (same tire, shorthand), 10.0/75-15.3 (flotation) or 23x8.50-12 (small/garden) and it will decode the width, aspect ratio, rim diameter and overall diameter.
Overall diameter here is a nominal figure calculated from the size designation, the same way it's labeled elsewhere on this site — not a tire maker's measured spec. For a specific tire's exact diameter, check that model's listing or the manufacturer's data sheet.
How to use the tire size converter
\nType the size exactly as it is molded on the sidewall into the tire size converter above, then compare the overall diameter with your current tire. Read tractor tire sizes explained for how each format works, or browse every size we list on the tire size pages.
Questions
Is 18.4-38 the same size as 18.4x38?
Yes. 18.4x38 and 18.4-38 are the same standard bias size written two different ways — the "x" is just shorthand some catalogs and dealers use instead of a dash. Both mean an 18.4-inch-wide tire for a 38-inch rim.
How do I convert a metric tractor tire size to the standard inch size?
There isn't a direct one-to-one conversion between metric (e.g. 420/85R28) and standard (e.g. 16.9-28) sizing — they're different systems, and a metric size doesn't always have an exact standard equivalent on the same rim. The two sizes that are commonly cross-referenced as closest equivalents are usually listed together in manufacturer fitment guides. This tool decodes each format on its own terms (width, aspect ratio, rim, overall diameter) so you can compare the resulting dimensions directly.
What does the overall diameter number actually tell me?
It tells you roughly how tall the tire stands and rolls, which matters for ground clearance, speedometer accuracy, and matching front and rear sizes (see our lead-lag calculator for MFWD tractors). It is a nominal figure calculated from the size, not a guaranteed measurement — tread wear, inflation and load all change the real rolling diameter slightly.