Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Outer diameter
28.52
inches
Sidewall height
5.76
inches
Circumference
89.6
inches
Revolutions per mile
707
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter section width (mm).
- 2Enter aspect ratio (%).
- 3Enter rim diameter (in).
- 4Read your outer diameter on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
Convert a P-metric tire code (e.g. 225/65R17) into physical dimensions.
Worked example
Using the values the calculator loads with:
Inputs
- Section width: 225 mm
- Aspect ratio: 65 %
- Rim diameter: 17 in
Results
- Outer diameter: 28.52
- Sidewall height: 5.76
- Circumference: 89.6
- Revolutions per mile: 707.26
What each field means
Inputs
- Section width (mm)
- The section width used in the calculation, measured in mm. Starts at 225 mm so you have a working example on load.
- Aspect ratio (%)
- The aspect ratio used in the calculation, measured in %. Starts at 65 % so you have a working example on load.
- Rim diameter (in)
- The rim diameter used in the calculation, measured in in. Starts at 17 in so you have a working example on load.
Results
- Outer diameter
- inches
- Sidewall height
- inches
- Circumference
- inches
- Revolutions per mile
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the tire size calculator work?
Convert a P-metric tire code (e.g. 225/65R17) into physical dimensions.
What do I need to enter?
3 values: section width, aspect ratio, and rim diameter. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the outer diameter result mean?
inches It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Tire Size Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/tire-size
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/tire-size" target="_blank" rel="noopener">Tire Size Calculator — RevenueLab</a> (2026).</p>
Source: [Tire Size Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/tire-size) (2026).