Metric & Inch Tire Size Converter
Convert metric or flotation tire markings into nominal millimeter and inch dimensions.
Enter a metric marking such as 275/35R19 or an inch marking such as 33x12.5R15.
Compare two tire sizes ↗These are dimensional conversions. They do not identify an equivalent manufactured tire or an approved vehicle fitment.
How to convert metric tire sizes to inches
Enter a metric marking such as 275/35R19, or a flotation marking such as 33x12.5R15. One inch equals 25.4 mm. For metric sizes, sidewall height is width × aspect ratio ÷ 100; overall diameter is twice that height plus the rim diameter converted to millimeters.
Worked example: 275/35R19
Sidewall height is 275 × 0.35 = 96.25 mm. Overall diameter is 2 × 96.25 + 19 × 25.4 = 675.1 mm, or 26.58 inches. Nominal section width is 10.83 inches; the rim remains 19 inches.
What does 33x12.5R15 mean?
It describes a nominal 33-inch overall diameter, 12.5-inch section width and 15-inch rim diameter. Those convert to 838.2 mm, 317.5 mm and 381 mm. Its nominal sidewall height is (33 − 15) ÷ 2 = 9 inches, or 228.6 mm.
Is the converted result an equivalent tire I can buy?
No. A calculated dimension does not establish a manufactured size or an approved replacement. Check the specific tire’s actual measurements, approved rim width, load and speed ratings, and vehicle requirements.
Why is the rim already in inches on a metric tire?
The marking combines units: section width is in millimeters, aspect ratio is a percentage, and rim diameter is in inches. Dividing every number by 25.4 would give the wrong result.
Dimension reference: Tire Rack’s tire dimension guide. Use the tire size comparison to compare two sizes after converting.