Tire size comparison calculator
Compare two tire sizes before you dig into fitment. See diameter, width, circumference and the nominal speedometer change side by side.
Supports radial metric sizes with widths of 100–995 mm, aspect ratios of 10–100, and rim diameters of 8–60 inches in whole or half inches. These are calculation bounds, not a claim that every size exists. Results use nominal unloaded geometry and do not confirm vehicle compatibility. Change the input or settings to update your result. Results update as you type. Up to 1,000,000 characters.
Your result
How to use Tire size comparison calculator
- Enter the reference and proposed metric tire sizes.
- Choose dimension and speed units, then enter an indicated speed.
- Compare the overlay and nominal changes, then download the table or report.
Useful next steps
Compare metric tire sizes
Enter a reference size and a proposed size, such as 205/55R16 and 225/45R17. The first number is section width in millimeters. The middle number is sidewall height as a percentage of width. The number after R is wheel diameter in inches. P, LT and ZR markings are accepted, but load indexes, speed-rating suffixes and flotation sizes such as 31x10.5R15 are outside this input format.
See what changes, in millimeters or inches
Sidewall height equals width × aspect ratio ÷ 100. Overall diameter adds two sidewalls to the wheel diameter, using exactly 25.4 millimeters per inch. Circumference is π × diameter. The overlay uses one shared scale for both sizes. The detailed table includes absolute and percentage changes, plus nominal revolutions per kilometer and mile.
Read the speedometer change in the right direction
The calculator assumes a speedometer calibrated exactly for the reference tire. With a larger proposed circumference, each revolution covers more distance, so nominal actual speed is higher than the displayed speed. With a smaller circumference, it is lower. For 205/55R16 to 225/45R17, an indicated 100 km/h corresponds to about 100.38 km/h under that assumption. Factory calibration error and loaded rolling radius are not included.
Treat clearance as a geometric estimate
Half the diameter change gives the nominal ride-height change and the opposite change in radial wheel-arch space. Half the width change reduces inner and outer space if the wheel centerline stays unchanged. These figures do not model wheel offset, rim width, suspension travel, tire-model differences, wear, pressure or load. They do not establish fitment, safety, approval or legality for a vehicle.
Keep the comparison
Download the comparison table as CSV, the overlay as SVG and the full calculation as a JSON report. The report includes unrounded values, assumptions and formula references. Everything is calculated in your browser; the tire sizes are not uploaded for processing.