Tyre Size Comparison Calculator
Enter width, aspect ratio, and rim diameter for two tire sizes to compare their theoretical nominal dimensions.
Use the three numbers printed in a tire size such as 205/55 R16. These are theoretical nominal dimensions, not vehicle fitment or speedometer safety advice.
Nominal comparison
A QUICK WALKTHROUGH
How to use this tool
- Enter the width, aspect ratio, and rim diameter for size A and size B.
- Compare nominal sidewall height, overall diameter, and circumference.
- Use the percentage difference as a dimensional reference only.
Nominal geometry
Sidewall = width × aspect ratio (%) ÷ 100. Overall diameter = rim diameter × 25.4 + 2 × sidewall. Circumference = π × overall diameter.
Interpret the result carefully
These calculations use nominal size markings and do not include tread variation, loaded radius, wheel width, suspension clearance, gearing, speedometer calibration, or legal requirements. Confirm fitment with the vehicle and tire manufacturer.
GOOD TO KNOW
Common questions
What does 205/55 R16 mean?
It means 205 mm width, a 55% aspect ratio, and a 16 inch rim diameter.
Are these measured tire dimensions?
No. They are theoretical nominal dimensions calculated from the printed size.
Can this confirm a replacement tire is safe?
No. Use it as a dimensional comparison and check vehicle manufacturer fitment guidance.