Everyday / Browser calculator

Tire Size Calculator

Tire Size Calculator works from the inputs you provide and returns sidewall (mm), diameter (mm), circumference (mm), revolutions/km. Use the calculation panel to explore a scenario, then check the formula and limitations before applying the result.

Free to useBrowser-based calculationFormula & example ↓

Your inputs

Minimum: 1
Minimum: 1 · Maximum: 100
Minimum: 1 · Maximum: 40

Your results

Enter your values and calculate to see the result.

Formula and calculation method

Sidewall = width × aspect/100. Diameter = 2×sidewall + rim×25.4. Circumference = π×diameter.

Nominal geometry; loaded rolling circumference and fitment clearances differ.

How to use tire size calculator

  1. Set Width (mm). The example below uses 205.
  2. Set Aspect ratio (%). The example below uses 55.
  3. Set Rim diameter (inches). The example below uses 16.
  4. Select Calculate to update the result. Reset restores the illustrated inputs. Copy, print or download your own result if you need a record.

Worked example

Example inputs
Width (mm)
205
Aspect ratio (%)
55
Rim diameter (inches)
16
Sidewall (mm)
112.75
Diameter (mm)
631.9
Circumference (mm)
1,985.1723978
Revolutions/km
503.73458804

Inputs and results explained

Tire Size Calculator takes 3 inputs. Fill each one using the same units and conventions, then select Calculate.

  • Width (mm): a number of 1 or more. The worked example uses 205.
  • Aspect ratio (%): a number from 1 to 100. The worked example uses 55.
  • Rim diameter (inches): a number from 1 to 40. The worked example uses 16.

The result panel reports Sidewall (mm), Diameter (mm), Circumference (mm) and Revolutions/km, so you can see the whole outcome rather than a single figure.

Factors affecting your result

Nominal geometry; loaded rolling circumference and fitment clearances differ.

Changing width (mm) changes the scenario being evaluated. Adjust one input at a time when comparing results, keep a copy of the assumptions, and compare values using the same unit and period. A precise arithmetic result does not make an uncertain assumption precise.

Frequently asked questions

How does the tire size calculator work?

Sidewall = width × aspect/100. Diameter = 2×sidewall + rim×25.4. Circumference = π×diameter.

What inputs does Tire Size Calculator need?

Enter width (mm), aspect ratio (%), rim diameter (inches). Read the unit labels; percentages are entered as ordinary percentages, not decimal fractions.

How should I interpret the tire size calculator result?

Nominal geometry; loaded rolling circumference and fitment clearances differ.

Are my tire size calculator inputs uploaded?

No. The calculation runs in this browser. Favorites, recent tool names, theme and formatting preferences may be saved locally, but calculation inputs are not sent to a calculation server or stored by this website. Shared links do not include entered values.

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