Tire Size Comparison Calculator
Put two tire sizes side by side to see the difference in diameter, width, sidewall and revolutions per mile, plus whether the swap stays inside the safe ±3% range.
Compare two tire sizes
Printed on the sidewall or on the driver door sticker.
Flotation sizes like 33×12.50R15 also work.
How to use the Tire Size Comparison Calculator
- Type your current size exactly as it appears on the sidewall, such as 225/45R17.
- Type the size you want to compare. Metric (P, LT) and flotation sizes like 33×12.50R15 are supported.
- Read the verdict. Green means the diameter change is within ±3%, the range most tire shops treat as safe.
- Check the full table for width, sidewall, circumference and revs-per-mile differences.
For the full background, read our guide: Can You Put Bigger Tires on Your Car? Plus-Sizing Explained.
The formula behind it
Diameter (mm) = Rim × 25.4 + 2 × Sidewall
Difference (%) = (New diameter − Old diameter) ÷ Old diameter × 100
Revs per mile = 1,609,344 ÷ (π × Diameter in mm)
Frequently asked questions
What difference in tire size is acceptable?
Most tire makers and shops recommend keeping the new overall diameter within 3% of the original. Within that range the speedometer, ABS and transmission behave almost exactly as designed.
Does a wider tire change the diameter?
Yes, if the aspect ratio stays the same. The sidewall is a percentage of the width, so a wider tire with the same aspect ratio is also taller.
Can I mix two different sizes on my car?
Only if your car came with a staggered setup from the factory. Mixing sizes on the same axle, or on all-wheel-drive cars, can damage the drivetrain.
Why does my result differ slightly from the tire maker’s spec?
This tool uses standard sizing math. Real tires vary by a few millimeters depending on brand, tread design and rim width.
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Results are estimates for general information only. Always confirm with your vehicle owner’s manual or a qualified technician before acting on them.