Tire size calculator
Know the size.
See the difference.
Turn a tire marking into dimensions. Compare a replacement with your original size before checking the details for your vehicle.
Calculated from the size marking. Actual tire dimensions vary by model and measuring conditions.
A measurement is
the starting point.
The calculator knows width, aspect ratio, and rim diameter. It cannot establish load capacity, speed rating, approved rim width, wheel offset, or clearance. Confirm those with your vehicle and tire specifications before installation.
Find your original size
Use the vehicle placard or owner’s manual to establish the baseline.
Start with the placardCompare the geometry
See two sizes at the same scale, their diameter change, and an estimated speed effect.
Compare two sizesExplore a larger rim
Find +1 and +2 rim candidates within the tool’s diameter filter.
Explore plus sizingThe calculation, in the open.
For a metric size, add the rim diameter to twice the sidewall height. Every number follows from that geometry.
Read the method and limitations →215/55R17 · nominal overall diameter
(17 × 25.4) + (2 × 215 × 0.55)
= 668.3 mm / 26.31 in
Explore tire dimensions
All sizes →Read the markings
Understand the numbers on the sidewall, what changes with a larger wheel, and where a size comparison stops.
How to read a tire size →Browse all guidesFrequently asked questions
What does 215/55R17 mean?
215 is the nominal section width in millimeters, 55 is the sidewall height as a percentage of width, R means radial construction, and 17 is the rim diameter in inches.
Is the calculator free?
Yes. Decode and compare tire sizes in your browser without an account. The displayed dimensions come from the size marking and basic geometry.
Are these measured tire dimensions?
No. These are nominal dimensions calculated from the size code. Actual dimensions and rolling circumference depend on the tire model, rim, inflation, load, and wear. Use the tire manufacturer’s specifications when choosing a product.
Does a small diameter difference mean a tire will fit?
No. A diameter percentage is a comparison of nominal sizes, not installation approval. Load index, speed rating, approved rim width, wheel offset, and physical clearance still need checking for your vehicle.
What is plus sizing?
Plus sizing pairs a larger rim diameter with a shorter tire sidewall to keep overall diameter close to the original. The plus-sizing tool lists geometric candidates; it does not verify product availability or vehicle fitment.
Add this calculator to your site — free
Run a car blog, forum, or shop site? Drop the tire size decoder into any page. It’s free, runs entirely in the visitor’s browser, and adds a small “Powered by TreadSize” credit that links back to us.