Sidewall to Diameter Car Tyres Tyres Size Chart
This chart converts tyre sizes from sidewall to diameter, covering 50 common tyre sizes. The table below shows the exact diameter for each sidewall measurement, helping you compare tyres across different notation systems.
Understanding both metric and imperial tyre measurements is important when shopping for replacements, especially if you are comparing tyres from different manufacturers or regions. Our chart covers standard passenger-car tyre sizes that you will find at most tyre retailers.
For example, a 4.4" tyre has a diameter of 24.9", while a 3.4" works out to 25.8".
Quick Converter
| Sidewall | Diameter |
|---|---|
| 4.0" | 22.1" |
| 4.2" | 22.4" |
| 4.5" | 22.8" |
| 4.7" | 23.2" |
| 4.5" | 24.0" |
| 4.7" | 24.5" |
| 5.0" | 25.0" |
| 5.3" | 25.5" |
| 4.0" | 23.0" |
| 4.2" | 23.4" |
| 4.4" | 23.7" |
| 4.6" | 24.2" |
| 4.4" | 24.9" |
| 4.7" | 25.3" |
| 4.9" | 25.7" |
| 4.8" | 25.7" |
| 5.1" | 26.2" |
| 5.3" | 26.6" |
| 3.8" | 24.6" |
| 4.0" | 25.0" |
| 4.2" | 25.3" |
| 4.3" | 25.7" |
| 4.2" | 25.5" |
| 4.4" | 25.9" |
| 4.7" | 26.3" |
| 4.9" | 26.7" |
| 5.1" | 27.2" |
| 3.5" | 25.1" |
| 3.7" | 25.4" |
| 3.9" | 25.7" |
| 4.0" | 26.0" |
| 4.0" | 26.0" |
| 4.2" | 26.3" |
| 4.3" | 26.7" |
| 4.6" | 27.3" |
| 5.1" | 28.2" |
| 3.2" | 25.5" |
| 3.4" | 25.8" |
| 3.5" | 26.0" |
| 3.9" | 26.7" |
| 4.0" | 27.0" |
| 4.3" | 27.7" |
| 4.5" | 28.0" |
| 3.4" | 26.8" |
| 3.5" | 27.0" |
| 3.8" | 27.6" |
| 3.9" | 27.7" |
| 4.0" | 28.0" |
| 4.3" | 28.7" |
| 4.5" | 29.0" |
How to Measure Your Tyres Size
Your tyre size is moulded into the sidewall and reads like 205/55R16. Split it into three parts: 205 is the section width in millimetres, 55 is the aspect ratio (sidewall height as a percentage of the width), and 16 is the wheel diameter in inches. You can also find the manufacturer's recommended size on the placard inside the driver's door jamb. These three figures are all you need to move between metric and inch-based measurements.
Tips for Converting Car Tyres Tyres Sizes
The aspect ratio (second number in metric notation) is a percentage of the tyre width. A 205/55R16 has a sidewall height of 55% of 205 mm = 112.75 mm.
Plus-sizing (fitting wider tyres on larger rims) is popular for appearance but can change ride quality. Keep the overall diameter within 3% of the original to maintain speedometer accuracy.
Never change tyre size without consulting your vehicle manufacturer's recommendations. An incorrect size can affect handling, braking distance, and speedometer accuracy.
Quick Reference
Quick reference: a 4.0" tyre has a diameter of 22.1", a 4.9" has a diameter of 26.7", and a 4.5" has a diameter of 29.0". See the full chart above for all 50 sizes.
This car tyres data is also available in Metric, Width sizing. Use the converter tool above to switch between any pair of systems instantly.
Frequently Asked Questions
- How do I read the sidewall tyre size notation?
- A metric tyre size like 4.9" has three parts: the first number is the width in millimetres, the second number (after the slash) is the aspect ratio as a percentage of the width, and the number after R is the rim diameter in inches. For example, 4.9" has a diameter of 26.7".
- Can I use a different tyre size than recommended?
- You should stick to sizes recommended by your vehicle manufacturer. Different sizes affect speedometer accuracy, braking distance, handling, and fuel economy. If you want to change sizes, consult a tyre specialist and keep the overall diameter within 3% of the original.
- What is the diameter of a 4.9" tyre?
- A 4.9" tyre has a diameter of 26.7". You can find the diameter for any of the 50 tyre sizes in our chart above.
- Where do I find my current tyre size?
- Your tyre size is printed on the sidewall of each tyre. You can also find the manufacturer-recommended size on the placard inside the driver's door jamb, in your owner's manual, or sometimes inside the fuel filler door.
- What does the R in tyre sizes mean?
- The R stands for Radial, which describes the internal construction of the tyre. Nearly all modern passenger-car tyres are radial. You may occasionally see D (diagonal/bias-ply) on trailer or vintage tyres.
- How many tyre sizes does this chart cover?
- This chart covers 50 common passenger-car tyre sizes, from 4.0" to 4.5", converting each from sidewall to diameter.