See a tire size every way it gets written
Enter a size in whichever notation you have it — metric or flotation — and see it converted into the other, plus a plain-inches breakdown of width, sidewall and rim.
Getting a number you can act on
- 01Enter the size in whatever notation you have it
Metric (225/65R17) and flotation (33x12.50R15) both work — the tool recognises either.
- 02Read the equivalent in the other notation
Both describe the same physical tire; converting between them makes a metric catalogue and a flotation spec directly comparable.
- 03Check the plain-inches breakdown for a tape-measure comparison
Width, sidewall and rim diameter in inches — useful when checking a size against a physical clearance measurement.
What the calculator is actually doing
Nothing here is proprietary. If you would rather check it by hand, or explain it to someone at a counter, these are the same expressions the tool evaluates.
flotation = diameter(in) X width(in) R rimFlotation notation states overall diameter and width directly in inches, rather than deriving them from a percentage.
metric = width(mm) / aspect-ratio R rimThe reverse direction, deriving an implied aspect ratio from the flotation size's stated diameter and width.
Two notations, one underlying set of dimensions
Metric notation states section width in millimetres and aspect ratio as a percentage, leaving overall diameter to be calculated. Flotation notation states overall diameter and width directly in inches, leaving aspect ratio implied rather than stated.
Neither is more correct — they are simply different starting points for describing the same three physical dimensions. This tool moves in whichever direction is needed, so a size read off one tire can be compared directly against a specification, catalogue listing or clearance measurement given in the other notation.
The conversion is exact geometry, not an approximation — both notations describe overall diameter, section width and rim diameter, and once any two of the underlying figures are known the third follows directly.
Tire Size Converter FAQ
How do I convert a metric tire size to flotation?+
Calculate the overall diameter and section width in inches from the metric size, then write them as diameter X width R rim — for example, 225/65R17 converts to approximately 28.5X8.9R17.
How do I convert a flotation tire size to metric?+
The flotation size already states diameter and width in inches; convert width to millimetres and derive the implied aspect ratio, then write as width/aspect-ratio R rim.
Is 285/70R17 the same as 33x12.50R17?+
Very close — 285/70R17 works out to about 32.7 inches overall diameter, within half an inch of a nominal 33. They are commonly cross-shopped for this reason, though the flotation size is usually slightly wider.
Which notation is more accurate?+
Neither — both describe the same physical dimensions from different starting points. Metric derives diameter from width and aspect ratio; flotation states diameter and width directly and leaves aspect ratio implied.
Standards and references behind these figures
The arithmetic on this page is fixed, but the boundaries and conventions around it come from published standards and manufacturer guidance. These are the documents they come from, so you can check them rather than take them on trust.
01The Tire and Rim Association — standards filing (NHTSA docket)TRA has been the US standardising body for tire and rim interchangeability since 1903; this filing sets out dimensional practice.↗02ISO 5775 — tire and rim designationsThe international designation system that sits alongside TRA and ETRTO practice.↗Nominal sizes, not measured ones. Every figure here is calculated from the size marked on the sidewall. Real tires vary from nominal by a few millimetres between manufacturers, and more as tread wears or pressure changes. Use these numbers to plan and to sanity-check a quote — measure the actual tire before committing to a tight fitment.