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Calculators / Automotive / Tire size
Tire size calculator
Calculate tire sidewall, overall diameter and circumference from metric size markings.
On this page
Sidewall height101.25mm
Overall diameter659.7mm
Circumference2,072.51mm
Calculator controls
How to calculate
Calculate tire sidewall, overall diameter and circumference from metric size markings.
Sidewall height = width*aspect/100; Overall diameter = rim*25.4+2*width*aspect/100; Circumference = pi*(rim*25.4+2*width*aspect/100)
Worked example
Section width (mm): 225; Aspect ratio (%): 45; Rim diameter (in): 18.
Sidewall height: 101.25 mm; Overall diameter: 659.7 mm; Circumference: 2,072.51 mm.
Assumptions and limits
Actual mounted dimensions vary by manufacturer, rim width, load and wear. Check clearance and approved fitment.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Calculate tire sidewall, overall diameter and circumference from metric size markings. The displayed figures use the inputs and formula shown on this page.
When this tool is useful
Use the tire size to compare a scenario, check an estimate, or verify a manual calculation.
Understanding your inputs
| Input | What to enter |
|---|---|
| Section width (mm) | Enter a number of at least 0.000001 and no more than 1000000000000. |
| Aspect ratio (%) | Enter a number of at least 1 and no more than 100. |
| Rim diameter (in) | Enter a number of at least 0.000001 and no more than 1000000000000. |
Frequently asked questions
What should I check before using the tire size result?
Actual mounted dimensions vary by manufacturer, rim width, load and wear. Check clearance and approved fitment.
Is this tire size result exact?
It is exact for the stated mathematical model and entered values. Real-world results can differ when rates, timing, fees, definitions or measurement conditions differ.