What is the Tire Size Calculator?
Calculate tire diameter, circumference and revolutions per mile from a size like 225/65R17. Tire size codes like 225/65R17 describe width, sidewall height and rim size, and converting them shows the real dimensions.
How to use the Tire Size Calculator
- Enter your width, your aspect ratio, your rim diameter.
- Results update automatically as you type; you can also press Calculate.
- Read the output: overall diameter, sidewall height, circumference, revolutions per mile.
- Use the 📊 chart to see the result visually, then copy or share it.
Formula and method
Worked example
With width = 225 mm, aspect ratio = 65 %, rim diameter = 17 in, the Tire Size Calculator returns overall diameter: 28.52 in; sidewall height: 5.76 in; circumference: 89.58 in.
Where the Tire Size Calculator helps in real life
You are upgrading to slightly larger tires. Comparing diameters shows how much your speedometer reading may change.
You are choosing between two tire sizes that fit your rims. Converting them shows the difference in overall height.
Common mistakes to avoid
- Ignoring speedometer changes.
- Choosing sizes that rub on suspension or fenders.
- Forgetting load and speed ratings.
- Mixing inches and millimeters.
💡 Practical tip: Larger tires make your speedometer read lower than your actual speed.
Tips for better results
- Check your vehicle’s recommended sizes.
- Compare overall diameter before buying.
- Ask a tire specialist about clearance.
Frequently asked questions
What does the Tire Size Calculator do?
Calculate tire diameter, circumference and revolutions per mile from a size like 225/65R17.
How is it calculated?
The Tire Size Calculator uses this method: Diameter = Rim + 2 × (Width × Aspect ÷ 25.4).
Can you show an example?
With width = 225 mm, aspect ratio = 65 %, rim diameter = 17 in, the Tire Size Calculator returns overall diameter: 28.52 in; sidewall height: 5.76 in; circumference: 89.58 in.
Is the Tire Size Calculator accurate?
Yes. It uses standard formulas and exact constants, and the results are verified by our automated test suite. Values are displayed to up to 12 significant digits.
Is this tool free and private?
Yes — the Tire Size Calculator is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
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