Tire Size Translator
Decode any metric tire size into plain English: width, sidewall height, overall diameter, load index and speed rating, plus a side-by-side size comparison.
Your tire size
What the code means
Dimensions
Overall diameter
How to read a tire size
Every tire has its size molded into the sidewall, in a code like 225/70R16 103T. It looks cryptic, but each part has a fixed meaning. This translator breaks the code apart and turns it into real measurements you can use when shopping, comparing or swapping wheels.
- 225 is the section width in millimetres.
- 70 is the aspect ratio: the sidewall height as a percentage of the width.
- R means radial construction.
- 16 is the wheel diameter in inches.
- 103 is the load index, the weight each tire can carry.
- T is the speed rating, the top speed the tire is built to sustain.
How the dimensions are calculated
Sidewall height is the width multiplied by the aspect ratio. For 225/70R16 that is 225 × 0.70 = 157.5 mm. The overall diameter is two sidewalls plus the wheel: 2 × 157.5 + 16 × 25.4 = 721 mm, or about 28.4 inches. Circumference and revolutions per kilometre follow from that diameter. Real tires vary slightly by brand and model, so treat these as nominal figures.
Comparing two sizes
Enter a second size to see how much bigger or smaller it is. Your speedometer is calibrated to the original diameter, so a taller tire makes it read low and a shorter one makes it read high. The comparison shows your true speed when the dial says 100 km/h.
Frequently asked questions
Can I put a different tire size on my car?
Often, yes, as long as the new size fits the wheel, clears the suspension and body, and meets the load and speed ratings your vehicle requires. Many shops try to keep the overall diameter within about 3% of the original. Always check your door placard or owner's manual and confirm with a tire professional.
What do the P and LT prefixes mean?
P marks a P-metric passenger tire built to US standards. LT marks a light truck tire designed for heavier loads. A size with no prefix is Euro-metric. P and Euro-metric tires of the same size can carry slightly different loads, so compare the load index rather than assuming they are identical.
Is a higher load index or speed rating always better?
Not necessarily. You need at least what your vehicle maker specifies. Going higher is safe, but it can mean a stiffer ride or a higher price. Never go below the specified load index.