Tire Size Calculator
Calculate tire diameter, sidewall height, circumference, and revolutions per mile from a tire size code like 215/65R16.
Total Diameter
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Sidewall Height
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Circumference
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Rev / Mile
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What is Tire Size Calculator?
A tire size calculator converts standard tire size codes (like 215/65R16) into actual measurements: total diameter, sidewall height, circumference, and revolutions per mile. This helps when comparing tire sizes, calculating speedometer accuracy, or planning wheel upgrades.
How to use
- 1 Either type the full tire code (e.g. 215/65R16) into the text field and click Parse, or
- 2 Enter the three values manually: section width in mm, aspect ratio %, and rim diameter in inches.
- 3 Click Calculate to see all tire dimensions.
- 4 Use revolutions per mile to check speedometer accuracy when switching tire sizes.
Formula
Example calculation
215/65R16: Sidewall = 215 × 0.65 = 139.75mm. Diameter = 16 + 2×(139.75/25.4) = 16 + 11.0 = 27.0 in. Circumference = π × 27.0 = 84.8 in. Rev/mile = 63,360 / 84.8 = 747.
Frequently asked questions
What do the numbers in a tire code mean?
215/65R16 means: 215 = section width in mm, 65 = aspect ratio (sidewall height as % of width), R = radial construction, 16 = rim diameter in inches.
How does tire size affect speedometer?
A larger diameter tire covers more distance per revolution, making your actual speed higher than the speedometer reads. A smaller tire does the opposite.
What is aspect ratio?
Aspect ratio is the sidewall height as a percentage of the tire's section width. A 65 aspect ratio means the sidewall height is 65% of 215mm = 139.75mm.
Can I put any tire size on my car?
No. Tire size is limited by wheel well clearance, load rating, and speed rating. Always check the manufacturer's recommended tire size range.
What is a plus-size tire upgrade?
A plus-size upgrade uses a wider tire with a lower aspect ratio on a larger rim, keeping the overall diameter nearly the same to preserve speedometer accuracy.