Tire Size Table: Overall diameter by Tyre width
Reference table of overall diameter for Tire Size across a range of tyre width values — exact, engine-computed figures you can read off at a glance.
Tire Size Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Overall diameter
24.88
- Sidewall height
- 112.8
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Tire Size Calculator
The Tire Size Calculator works out your overall diameter, along with 1 related figure in an instant. Enter tyre width, aspect ratio and rim diameter and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the tyre width.
- Enter the aspect ratio.
- Enter the rim diameter.
- Read off your overall diameter, together with sidewall height — the calculator updates automatically, with no button to press.
Formula
The Tire Size Calculator uses the formula:
Overall diameter = Rim diameter + 2 × (Tyre width × Aspect ratio ÷ 100) ÷ 25.4
Worked example
For example, with tyre width of 205 mm, aspect ratio of 55 % and rim diameter of 16 in, the overall diameter is 24.88.
| Tyre width | 205 mm |
|---|---|
| Aspect ratio | 55 % |
| Rim diameter | 16 in |
| Overall diameter | 24.88 |
|---|---|
| Sidewall height | 112.8 |
Results are estimates for educational use, not professional advice.
Key terms explained
- Diameter
- The distance across a circle through its centre — twice the radius.
- Ratio
- A comparison of two quantities showing how many times one contains the other.
Frequently asked questions
A size like 205/55 R16 means 205 mm wide, a sidewall 55% of the width, on a 16-inch rim. That tyre is about 24.9 inches in overall diameter.
It is the sidewall height as a percentage of the tread width. A lower number means a shorter, sportier sidewall.
Changing diameter affects your speedometer reading, gearing and clearance. Keep replacements within about 3% of the original diameter.
Multiply the width by the aspect ratio percentage. For 205/55, the sidewall is 205 × 0.55 = 112.75 mm.
The Tire Size Calculator uses the formula: Overall diameter = Rim diameter + 2 × (Tyre width × Aspect ratio ÷ 100) ÷ 25.4. For example, with tyre width of 205 mm, aspect ratio of 55 % and rim diameter of 16 in, the overall diameter is 24.88.
Related guides
How to Calculate Tire Size: Formula, Steps & Examples
Learn how to calculate Tire Size — the formula explained step by step, with worked examples and a free calculator to check your answer.