02 / TIRE TOOLS
Tire Size Calculator
Nominal tire dimensions.
What changes
NOMINAL GEOMETRYExample calculation. Replace these values with your setup.
Nominal tire geometry
Nominal tire geometry
See the tire measurements
Diameter
- Your setup
- 634.3 mm
Across the whole tire, from one outside edge to the other. This is the unloaded diameter.
01Your setup
| Measurement | Value |
|---|---|
| 634.3 mm | |
| 225.0 mm | |
| 101.3 mm | |
| Unloaded radius | 317.2 mm |
| Geometric circumference | 1,992.7 mm |
| Estimated revolutions / km | 501.8 |
| Estimated revolutions / mile | 807.6 |
Assumptions & limits
- Markings describe nominal geometry. Actual tire dimensions vary by tire model, measuring rim, pressure, and wear.
- Unloaded radius and geometric circumference do not measure loaded ride height or actual rolling circumference.
- Load and speed markings and approved tire-to-rim width combinations are not evaluated by these geometry calculations.
Read a tire size marking
Decode a metric or flotation tire (tyre) size into nominal diameter, section width, sidewall height and circumference.
Example · 225/45R17
The marking gives a nominal section width of 225 mm, sidewall height of 101.25 mm and overall diameter of 634.3 mm. The theoretical circumference is about 1,992.7 mm.
These are dimensions from the size marking; use manufacturer specifications or measurements for the actual tire envelope.
Tire size questions
What do 225, 45 and R17 mean?
225 is the nominal section width in millimeters. 45 is the sidewall height as a percentage of that width. R indicates radial construction, and 17 is the matching wheel rim diameter in inches.
Can I enter a flotation size such as 33x12.50R15?
Yes. A flotation marking gives nominal overall diameter and section width in inches, followed by the wheel rim diameter. This tool converts the same geometry to metric or imperial display units.
Are the calculated revolutions a manufacturer specification?
No. Revolutions per distance are derived from the theoretical free circumference. Rolling deformation, tire pressure, load, wear and construction can change the distance traveled per revolution.
Methodology & limits
How this tool works
Metric sidewall height = section width × aspect ratio / 100. Nominal diameter = rim diameter × 25.4 + twice the sidewall height. Circumference = π × diameter.