Tire Size Calculator
Work out a tire’s sidewall height, overall diameter and circumference from its width, aspect ratio and rim size — useful when comparing tire sizes.
Nominal unloaded geometry only. Real rolling circumference varies with pressure, load, wear and construction. A ±3% comparison is only a screening check—verify rim width, load/speed ratings, clearance and manufacturer approval.
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Tire size calculator
Parse metric, P/LT and flotation tire sizes, compare nominal dimensions in millimeters and inches, and estimate speedometer and odometer effects.
FAQ
Which tire formats can I enter?
Metric P/LT forms such as 205/55R16, P205/55R16 and LT265/70R17, plus flotation sizes such as 31×10.50R15.
What do the numbers mean?
For 205/55R16: 205 is nominal section width in mm, 55 is the sidewall aspect percentage, and 16 is the rim diameter in inches.
How is the diameter calculated?
Overall diameter = rim (in mm) + 2 × sidewall, where sidewall = width × aspect ÷ 100.
How are speedometer and odometer errors calculated?
Actual speed and distance = indicated value × new circumference ÷ original circumference. Positive means the vehicle travels faster and farther than indicated.
Are these real rolling dimensions?
No. These are nominal unloaded dimensions. Tire pressure, load, tread wear and manufacturer construction change real rolling circumference.
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