Tire Size Calculator

Compare two tire sizes: diameter, sidewall, circumference and speedometer error.

Current tire
New tire

How the calculation works

Sidewall height = width × aspect ratio ÷ 100. Overall diameter = rim diameter × 25.4 + 2 × sidewall. Circumference = π × diameter. When the new tire is larger, each wheel revolution covers more distance, so the car travels faster than the speedometer shows. Keep the difference within about ±3% and check approved sizes for your vehicle.

Looking for a common size? Browse the tire size chart.

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