Tire Size Calculator

Use the calculators below to compute tire dimensions from a code like 265/70R17, and compare two sizes side by side. Modify values and click Calculate.

Tire Size

Find dimensions of a tire from its code or by entering values.

Tire Size Comparison

Compare two sizes numerically and visually.

Tire 1

Tire 2

Tire Code — How to Read It

Tire code diagram showing all parts of a tire sidewall including size, load index, speed rating, and DOT code

Visual guide to reading tire sidewall markings

Car tires are labeled with an alphanumeric code such as 265/70R17. Each part describes a tire characteristic:

  • Intended use: P (Passenger), LT (Light Truck), ST (Special Trailer), T (Temporary/spare).
  • Nominal section width: three digits in mm (e.g., 265).
  • Aspect ratio: two or three digits after "/" showing sidewall height as % of width (e.g., 70 → 70%).
  • Internal construction: R (Radial), D (Diagonal), B (Bias-belted).
  • Wheel diameter: one or two digits in inches (e.g., 17).
  • Load index & Speed rating: e.g., 115H — max load at a rated speed.
  • DOT code: includes the manufacture date (e.g., "1324" = 13th week of 2024). Older than ~6–10 years is generally not recommended.

Formulas Used

  • Section Height = Width × (Aspect / 100)
  • Overall Diameter = Rim + 2 × Section Height
  • Circumference = π × Diameter
  • Revs per mile = 63,360 in ÷ Circumference

When changing sizes, a common guideline is to keep overall diameter within about ±3% of your stock size to reduce speedometer error and suspension/ABS impacts.