Tyre Size Conversion Chart
Compare calculated nominal tyre circumferences when researching a different wheel diameter or tyre profile.
How to Use the Chart
Each row retains the original comparison sizes. They are not all equivalent: the figures beneath each size show its calculated nominal circumference and percentage difference from the first size in that row. A small percentage difference alone does not establish suitability.
Changing tyre size can affect speedometer accuracy, gearing, clearance, handling, load capacity and insurance. The chart is a starting point only—it does not confirm that a size is suitable for a particular vehicle or wheel.
| 155/65/13 1670.4 mm Reference | 185/55/13 1676.7 mm +0.38% | 185/50/14 1698.3 mm +1.67% | 195/45/14 1668.5 mm -0.11% | 195/45/15 1748.3 mm +4.66% | 195/40/16 1766.8 mm +5.77% | |
| 175/60/14 1776.9 mm Reference | 185/55/14 1756.5 mm -1.15% | 195/45/15 1748.3 mm -1.61% | 195/40/16 1766.8 mm -0.57% | 205/40/16 1792.0 mm +0.85% | 195/45/16 1828.1 mm +2.88% | |
| 205/65/15 2034.2 mm Reference | 225/55/16 2054.3 mm +0.99% | 235/45/17 2021.0 mm -0.65% | 235/40/18 2027.0 mm -0.36% | 265/35/18 2019.1 mm -0.74% | 245/35/19 2054.9 mm +1.02% | 275/30/19 2034.5 mm +0.02% |
| 185/60/14 1814.6 mm Reference | 195/50/15 1809.6 mm -0.28% | 215/50/15 1872.4 mm +3.19% | 215/40/16 1817.1 mm +0.14% | 195/45/16 1828.1 mm +0.74% | 195/40/17 1846.6 mm +1.77% | 205/40/17 1871.8 mm +3.15% |
| 195/60/14 1852.3 mm Reference | 195/55/15 1870.8 mm +1.00% | 205/50/15 1841.0 mm -0.61% | 205/45/16 1856.4 mm +0.22% | 205/40/17 1871.8 mm +1.05% | 215/35/18 1909.1 mm +3.07% | 225/35/18 1931.1 mm +4.26% |
| 195/60/15 1932.1 mm Reference | 205/50/16 1920.8 mm -0.59% | 215/40/17 1896.9 mm -1.82% | 215/35/18 1909.1 mm -1.19% | 225/35/18 1931.1 mm -0.05% | 215/35/19 1988.9 mm +2.94% | 225/35/19 2010.9 mm +4.08% |
| 205/60/15 1969.8 mm Reference | 205/55/16 1985.2 mm +0.78% | 225/45/17 1992.7 mm +1.16% | 225/40/18 2001.8 mm +1.63% | 255/35/18 1997.1 mm +1.39% | 235/35/19 2032.9 mm +3.21% | 265/30/19 2015.6 mm +2.33% |
| 225/55/17 2134.1 mm Reference | 235/50/18 2174.6 mm +1.90% | 245/45/18 2129.1 mm -0.24% | 245/40/19 2131.9 mm -0.10% | 275/35/19 2120.9 mm -0.62% | 245/35/20 2134.7 mm +0.03% | 285/30/20 2133.1 mm -0.04% |
| 275/55/17 2306.9 mm Reference | 255/55/18 2317.6 mm +0.46% | 285/50/18 2331.7 mm +1.08% | 255/50/19 2317.2 mm +0.45% | 275/40/20 2287.1 mm -0.86% | 265/35/22 2338.3 mm +1.36% | 295/30/22 2311.6 mm +0.20% |
| 275/60/17 2393.3 mm Reference | 285/55/18 2421.2 mm +1.17% | 255/55/19 2397.3 mm +0.17% | 265/50/20 2428.5 mm +1.47% | 275/45/20 2373.5 mm -0.83% | 295/45/20 2430.0 mm +1.54% | 285/35/22 2382.3 mm -0.46% |
Calculation: diameter in millimetres = wheel diameter in inches × 25.4 + 2 × tyre width × aspect ratio ÷ 100. Nominal circumference = diameter × π. Actual rolling circumference depends on the tyre and operating conditions. Scroll sideways on smaller screens.