Common Tire Sizes Chart: Diameter, Width and Sidewall in Inches

The chart

Calculated from each size code. Revolutions per mile are calculated from the free diameter; tire makers publish measured figures for each model, which can differ.

How the numbers are calculated

For metric sizes: sidewall = width (mm) × aspect ratio ÷ 100 ÷ 25.4; diameter = 2 × sidewall + wheel size; revolutions per mile = 63,360 ÷ (π × diameter). Flotation sizes such as 33x12.50R15 state diameter and width in inches directly. The size calculator shows the working for any size.

Using the chart to compare sizes

Find your current size and look for sizes with a similar diameter. Continental's plus-sizing bulletin says that keeping rolling circumference within ±3% usually needs no adjustments to speedometer, ABS or stability systems. On a 28.5 inch tire, 3% is about 0.86 inches; on a 31.6 inch tire it is about 0.95 inches.

Some patterns stand out in the chart:

• Same wheel, wider tire, same aspect ratio means a taller tire too: 265/70R17 to 285/70R17 adds about 1.1 inches of diameter, because the sidewall is a percentage of width.
• Bigger wheel, lower aspect ratio can keep the diameter close: 205/55R16 and 225/45R17 differ by less than half a percent.
• Flotation sizes for trucks are listed by diameter, so a "33" is about 33 inches tall when calculated, while measured sizes can vary.

For exact percentages and a speedometer reading, use the comparison tool.

Metric widths in inches

What this chart is not

It is not a fitment guide. Whether a size fits a particular vehicle depends on the wheel width and offset, brake and suspension clearance and the vehicle maker's approval, and the load index and speed rating must meet the original tires' ratings. NHTSA advises buying the size on your vehicle's placard or another size the vehicle manufacturer recommends, and asking a tire dealer if in doubt. Our plus sizing guide explains the checks.

Finding your size

Your current tires show their size on the sidewall; the original size is on the door label. See how to read a tire sidewall for every marking.

Common questions

What size is a 265/70R17 in inches?

About 31.6 inches tall and 10.4 inches wide on a 17 inch wheel, with a 7.3 inch sidewall.

Is a 275/65R18 the same as a 33 inch tire?

Its calculated diameter is about 32.1 inches, so it is close to but smaller than 33 inches. Use the comparison tool to see the exact difference against a 33x12.50R15 or any other size.

Why do two tires of the same size measure differently?

Tread design, construction and the rim width used for measuring all affect real dimensions. Tire makers publish measured diameter and revolutions per mile for each model and size.

Which size is right for my car?

The size printed on the Tire and Loading Information label on the driver's door edge or post, or in the owner's manual. NHTSA recommends the original size or another size the vehicle maker recommends.