tiresizeinches.com

Metric → inches

Read any tire size in inches

Type the three numbers off the sidewall. The gauge below is drawn to scale, so you see the tire as well as the figure.

mm, 115–395
% of width
inches

Reading 275/65R20. Change any field and the gauge follows.

Overall diameter

34.07in

A 275/65R20 tire stands 34.07 in (865.5 mm) tall, measures 10.83 in across the section and turns 591.9 times per mile.

Section width
10.83 in275 mm
Sidewall
7.04 in178.8 mm
Wheel
20 in508.0 mm
275/65R20 drawn to scaleA 275/65R20 tire drawn to scale, seen from the side and head-on at one scale. Four dimension lines label the overall diameter 34.07 in, the wheel diameter 20 in, the sidewall height 7.04 in and the section width 10.83 in. Every one of those values is stated in text on this page.34.07 in20 in wheel7.04 in10.83 in
Drawn to scale from the three numbers above. The side view and the head-on section share one scale.

The sizes people look up most

Each one already computed, on its own page.

The arithmetic, in full

One formula, one constant, no lookup table.

// overall diameter, inches
diameter = wheel + (width × aspect × 2) ÷ 2540
         = 20 + (275 × 65 × 2) ÷ 2540
         = 20 + 14.07
         = 34.07 in

section  = width ÷ 25.4 = 10.83 in
sidewall = width × aspect ÷ 100 ÷ 25.4 = 7.04 in
revs/mi  = 63360 ÷ (π × diameter) = 591.9

Two sidewalls, in inches, are 2 × width × aspect ÷ (100 × 25.4), so the constant is exactly 2540. Charts that round it to 2550come out short, and the gap widens as diameters grow.

  • Sizes are nominal. A molded tire varies from its stated size by manufacturer.
  • Unloaded diameter. Under load the rolling radius is smaller.
  • Rim width, load index and speed rating are not in the sidewall code and are not calculated here.
  • This is a dimensional calculation, not a fitment guarantee.