245/55R18 Tire Size in Inches & Millimeters

Tire size “245/55R18” indicates your vehicle’s specifications based on tire width, aspect ratio, height, tire construction, diameter, radial and inches. These tire size numbers represent our tire sizes in both Metric (in millimeters) and Imperial (in inches) units of measurement to help find the correct tire size for your vehicle.

To convert tire size 245/55R18 to inches, you must know what these numbers represent.

So let us know 245/55R18 in simple words:

First number “245” indicates the tire’s width in millimeters.
Second number “55” refers to the aspect ratio, which is the height of the tire’s sidewall as a percentage of its width.
Third number “R18” refers to a tire that is designed to fit a 18-inch diameter rim.

Therefore, when converting the tire size 245/55R18 to inches, it can be concluded that the width of the tire will be approximately 9.6 inches ( 245 mm= 9.6 in), and the sidewall height will be approximately 5.3 inches (55% of 9.6 inches = 5.3 inches).

How to convert 245/55R18 into Inches (imperial)?

To convert tire size 245/55R18 to inches (Imperial) –

1. Width conversion: To convert it to inches, you can use a conversion factor of approximately 25.4 millimeters per inch.

  • 245 millimeters/25.4 = approximately 9.6 inches
    So, the width of the tire is approximately 9.6 inches.

2. Aspect Ratio Calculation: To calculate sidewall height in inches, you can use the tire width (from Step 1) and the aspect ratio:

  • Sidewall Height = Width (in inches) * Aspect Ratio / 100
  • Sidewall Height = 9.6 inches * 55/100 = approximately 5.3 inches
    So, the tire sidewall height is approximately 5.3 inches.

3. Rim Diameter: The “R” in the tire size stands for “radial construction” and the last number “18” indicates the rim diameter in inches. In this case, it’s already in inches.
So, the converted tire size “245/55R18” in inches (imperial) is approximately:

  • Width: 9.6 inches
  • Sidewall Height: 5.3 inches
  • Rim Diameter: 18 inches

How to convert 245/55R18 into Millimeters (metric)?

To convert the tire size 245/55R18 into millimeters (metric) –

1. Width Conversion: The first number in the tire size, “245“, represents the tire’s width in millimeters. Since it’s already in millimeters, there’s no need for conversion.

  • Width: 245millimeters

2. Aspect Ratio Calculation: The second number “55” is the aspect ratio, representing the tire’s sidewall height as a percentage of its width. To calculate the sidewall height in millimeters, you can use the tire’s width (from step 1) and the aspect ratio:

  • Sidewall height = Width (in millimeters) * Aspect Ratio / 100
  • Sidewall height = 245 millimeters * 55 / 100 = 135 mm millimeters
    So, the tire’s sidewall height is approximately 135 mm millimeters.

3. Rim Diameter: The “R” in the tire size stands for “radial construction” and the last number, “18” indicates the rim diameter in inches. To convert this to millimeters, you can use the conversion factor of approximately 25.4 millimeters per inch.

  • Rim diameter = 18 inches * 25.4 millimeters per inch = 457 mm millimeters
    So, the rim diameter is approximately 457 mm millimeters.

So, the converted tire size “245/55R18” in millimeters (metric) is approximately:

  • Width: 245 mm
  • Sidewall Height: 135 mm
  • Rim Diameter: 457 mm

Alternate Tire Size of 245/55R18 For replacement

Tire Size Overall Diameter Difference
165/60R20 27.8″ (706 mm) -2.9%
285/35R20 27.9″ (708 mm) -2.6%
315/40R18 27.9″ (709 mm) -2.5%
155/65R20 28″ (710 mm) -2.3%
335/30R20 28″ (710 mm) -2.3%
225/45R20 28″ (710 mm) -2.3%
285/40R19 28″ (711 mm) -2.2%
255/40R20 28″ (712 mm) -2.1%
285/45R18 28.1″ (713 mm) -1.9%
255/45R19 28.1″ (713 mm) -1.9%
255/50R18 28.1″ (713 mm) -1.9%
295/35R20 28.1″ (714 mm) -1.8%
235/55R18 28.1″ (715 mm) -1.7%
145/80R19 28.1″ (715 mm) -1.7%
345/30R20 28.2″ (716 mm) -1.5%
235/50R19 28.3″ (719 mm) -1.1%
295/40R19 28.3″ (719 mm) -1.1%
265/40R20 28.3″ (720 mm) -1%
235/45R20 28.3″ (720 mm) -1%
155/85R18 28.4″ (721 mm) -0.8%
265/45R19 28.4″ (721 mm) -0.8%
305/35R20 28.4″ (722 mm) -0.7%
265/50R18 28.5″ (723 mm) -0.6%
295/45R18 28.5″ (723 mm) -0.6%
345/35R19 28.5″ (725 mm) -0.3%
225/60R18 28.6″ (727 mm) 0%
315/35R20 28.7″ (728 mm) 0.1%
275/40R20 28.7″ (728 mm) 0.1%
245/45R20 28.7″ (728 mm) 0.1%
245/50R19 28.7″ (729 mm) 0.3%
275/45R19 28.8″ (731 mm) 0.6%
155/80R19 28.8″ (731 mm) 0.6%
225/55R19 28.8″ (731 mm) 0.6%
305/45R18 28.8″ (731 mm) 0.6%
275/50R18 28.9″ (733 mm) 0.8%
315/40R19 28.9″ (735 mm) 1.1%
325/35R20 29″ (736 mm) 1.2%
285/40R20 29″ (736 mm) 1.2%
175/80R18 29″ (737 mm) 1.4%
155/90R18 29″ (737 mm) 1.4%
255/55R18 29″ (737 mm) 1.4%
255/45R20 29.1″ (738 mm) 1.5%
285/45R19 29.1″ (739 mm) 1.7%
255/50R19 29.1″ (739 mm) 1.7%
235/60R18 29.1″ (739 mm) 1.7%
145/80R20 29.1″ (740 mm) 1.8%
235/55R19 29.2″ (741 mm) 1.9%
285/50R18 29.3″ (743 mm) 2.2%
235/50R20 29.3″ (744 mm) 2.3%
295/40R20 29.3″ (744 mm) 2.3%
265/45R20 29.4″ (746 mm) 2.6%

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