205/40R18 Tire Size in Inches and Millimeters

205/40R18 tires have a diameter of 24.4" (621 mm), a tread width of 8.1" (205 mm), and a wheel diameter of 18" (457.2 mm).The sidewall of the tire is 3.2" (82 mm), and the tire's circumference is 76.6" (1949.9 mm). This means a 205/40R18 tire will make make 827 revolutions per mile, or 513 revolutions per kilometer.

205/40R18 Tire Front
8.1"
24.4"
205/40R18 Tire Side
Tire Circumference
76.6"
18"
3.2"
827 Revs/Mile
SpecInchesMetric
Diameter24.4"621 mm
Width8.1"205 mm
Wheel18"457.2 mm
Sidewall3.2"82 mm
Circum76.6"1949.9 mm
Revolutions827 per mile513 per km

What Does 205/40R18 Mean?

The tire size 205/40R18 is a common size used on many trucks, SUVs, and other larger vehicles.

Here is what each part of the size designation represents:

  • 205: This number represents the width of the tire in millimeters. In this case, the tire is 205 millimeters wide.
  • 40: This number represents the aspect ratio of the tire, which is the height of the tire's sidewall as a percentage of its width. In this case, the sidewall height is 40% of the tire's width.
  • R: This letter indicates the tire's construction type. “R” stands for radial construction, which is the most common type of tire construction today.
  • 18: This number represents the diameter of the wheel that the tire is designed to fit on, in inches. In this case, the tire is designed to fit on a 18-inch wheel.

205/40R18 tire size meaning

How To Convert 205/40R18 Into Inches

The 205/40R18 conversion is fairly simple. The first number in the tire size, 205, represents the width of the tire in millimeters. To convert this to inches, we divide 205 by 25.4 (since there are 25.4 millimeters in an inch). This gives us approximately 8.1 inches.

The second number in the tire size, 40, represents the aspect ratio or the height of the tire as a percentage of its width. To calculate the height in inches, we multiply 8.1 by 0.40, which gives us approximately 3.2 inches.

Finally, the last number in the tire size, 18, represents the diameter of the wheel rim in inches. Therefore, the tire size 205/40R18 can be expressed in inches as roughly 8.1 inches wide, 3.2 inches tall, and designed to fit a 18-inch wheel rim.

Frequently Asked Questions About 205/40R18 Tires

How tall is a 205/40R18 tire?

A 205/40R18 tire has an approximate height, also known as the overall diameter, of 24.4 inches (621 mm). This height can vary slightly depending on the brand and model of the tire, as well as the amount of air pressure in the tire.

How wide is a 205/40R18 tire?

A 205/40R18 tire has a width of approximately 8.1 inches (205 millimeters). The width of the tire is the first number in the tire size designation, which in this case is “205”. It’s important to note that the actual width of the tire may vary slightly depending on the brand and model of the tire, and the width may also be affected by the amount of air pressure in the tire.

Alternate 205/40R18 Replacement Tire Sizes

Upsizing your wheels or tires? Replacement tires must be within 3% of the diametor of the original tire. The following sizes fall within that range - click on any size to see detailed info about that tire and wheel combination.

SizeDiameterWidthWheel
125/60R1823.9"607 mm18 mm
125/70R1723.9"608 mm17 mm
125/70R1824.9"633 mm18 mm
125/80R1623.9"606 mm16 mm
125/80R1724.9"632 mm17 mm
125/85R1624.3"618 mm16 mm
125/90R1523.9"607 mm15 mm
125/90R1624.9"632 mm16 mm
135/60R1824.4"619 mm18 mm
135/70R1724.5"622 mm17 mm
135/80R1624.5"622 mm16 mm
135/90R1524.6"625 mm15 mm
145/70R1725"636 mm17 mm
145/80R1625.1"638 mm16 mm
155/80R1423.8"604 mm14 mm
155/80R1524.8"629 mm15 mm
165/80R1424.4"620 mm14 mm
175/45R1824.2"615 mm18 mm
175/55R1724.6"624 mm17 mm
175/60R1624.3"616 mm16 mm
175/65R1524"609 mm15 mm
175/70R1524.7"627 mm15 mm
175/75R1424.3"618 mm14 mm
175/80R1324"610 mm13 mm
175/80R1425"636 mm14 mm
185/50R1724.3"618 mm17 mm
185/55R1624"610 mm16 mm
185/60R1523.7"603 mm15 mm
185/60R1624.7"628 mm16 mm
185/65R1524.4"621 mm15 mm
185/70R1424.3"616 mm14 mm
185/75R1425"634 mm14 mm
185/80R1324.6"626 mm13 mm
195/45R1723.9"608 mm17 mm
195/50R1724.7"628 mm17 mm
195/55R1624.4"620 mm16 mm
195/60R1524.2"615 mm15 mm
195/65R1424"610 mm14 mm
195/65R1525"635 mm15 mm
195/70R1323.8"604 mm13 mm
195/70R1424.8"630 mm14 mm
205/40R1824.4"621 mm18 mm
205/45R1724.3"616 mm17 mm
205/50R1624.1"612 mm16 mm
205/50R1725.1"638 mm17 mm
205/55R1523.9"607 mm15 mm
205/55R1624.9"632 mm16 mm
205/60R1524.7"627 mm15 mm
205/65R1424.5"622 mm14 mm
205/70R1324.3"618 mm13 mm
215/30R2025.1"638 mm20 mm
215/35R1823.9"607 mm18 mm
215/35R1924.9"633 mm19 mm
215/40R1723.8"604 mm17 mm
215/40R1824.8"629 mm18 mm
215/45R1724.6"626 mm17 mm
215/50R1624.5"622 mm16 mm
215/55R1524.3"617 mm15 mm
215/60R1424.2"614 mm14 mm
215/60R1525.2"639 mm15 mm
215/65R1425"636 mm14 mm
225/30R1924.4"619 mm19 mm
225/35R1824.2"615 mm18 mm
225/40R1724.1"612 mm17 mm
225/40R1825.1"637 mm18 mm
225/45R1623.9"608 mm16 mm
225/45R1725"634 mm17 mm
225/50R1523.9"607 mm15 mm
225/50R1624.9"632 mm16 mm
225/55R1423.8"604 mm14 mm
225/55R1524.8"629 mm15 mm
225/60R1424.6"626 mm14 mm
235/30R1924.6"625 mm19 mm
235/35R1824.4"621 mm18 mm
235/40R1724.4"620 mm17 mm
235/50R1524.3"617 mm15 mm
235/55R1525.2"639 mm15 mm
235/60R1324.1"612 mm13 mm
235/60R1425.1"638 mm14 mm
245/30R1823.8"605 mm18 mm
245/30R1924.8"631 mm19 mm
245/35R1723.8"604 mm17 mm
245/35R1824.8"629 mm18 mm
245/40R1724.7"628 mm17 mm
245/45R1624.6"626 mm16 mm
245/50R1524.7"627 mm15 mm
255/30R1824.1"611 mm18 mm
255/30R1925.1"637 mm19 mm
255/35R1825"635 mm18 mm
255/40R1725"636 mm17 mm
255/45R1524.1"611 mm15 mm
255/55R1425"636 mm14 mm
265/30R1824.3"617 mm18 mm
265/35R1724.3"618 mm17 mm
265/50R1424.5"622 mm14 mm
275/35R1724.6"624 mm17 mm
285/30R1824.8"629 mm18 mm
285/35R1724.9"632 mm17 mm
285/40R1524"609 mm15 mm
295/25R1924.8"631 mm19 mm
295/30R1825"635 mm18 mm
295/35R1725.1"638 mm17 mm
305/25R1925"635 mm19 mm
345/35R1524.5"623 mm15 mm