315/30R18 Tire Size in Inches & Millimeters

Tire size “315/30R18” 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 315/30R18 to inches, you must know what these numbers represent.

So let us know 315/30R18 in simple words:

First number “315” indicates the tire’s width in millimeters.
Second number “30” 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 315/30R18 to inches, it can be concluded that the width of the tire will be approximately 12.4 inches ( 315 mm= 12.4 in), and the sidewall height will be approximately 3.7 inches (30% of 12.4 inches = 3.7 inches).

How to convert 315/30R18 into Inches (imperial)?

To convert tire size 315/30R18 to inches (Imperial) –

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

  • 315 millimeters/25.4 = approximately 12.4 inches
    So, the width of the tire is approximately 12.4 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 = 12.4 inches * 30/100 = approximately 3.7 inches
    So, the tire sidewall height is approximately 3.7 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 “315/30R18” in inches (imperial) is approximately:

  • Width: 12.4 inches
  • Sidewall Height: 3.7 inches
  • Rim Diameter: 18 inches

How to convert 315/30R18 into Millimeters (metric)?

To convert the tire size 315/30R18 into millimeters (metric) –

1. Width Conversion: The first number in the tire size, “315“, represents the tire’s width in millimeters. Since it’s already in millimeters, there’s no need for conversion.

  • Width: 315millimeters

2. Aspect Ratio Calculation: The second number “30” 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 = 315 millimeters * 30 / 100 = 95 mm millimeters
    So, the tire’s sidewall height is approximately 95 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 “315/30R18” in millimeters (metric) is approximately:

  • Width: 315 mm
  • Sidewall Height: 95 mm
  • Rim Diameter: 457 mm

Alternate Tire Size of 315/30R18 For replacement

Tire Size Overall Diameter Difference
285/30R18 24.8″ (629 mm) -2.8%
215/40R18 24.8″ (629 mm) -2.8%
245/35R18 24.8″ (629 mm) -2.8%
295/25R19 24.8″ (631 mm) -2.5%
245/30R19 24.8″ (631 mm) -2.5%
215/35R19 24.9″ (633 mm) -2.2%
125/70R18 24.9″ (633 mm) -2.2%
255/35R18 25″ (635 mm) -1.9%
305/25R19 25″ (635 mm) -1.9%
295/30R18 25″ (635 mm) -1.9%
225/40R18 25.1″ (637 mm) -1.5%
255/30R19 25.1″ (637 mm) -1.5%
215/30R20 25.1″ (638 mm) -1.4%
205/45R18 25.2″ (641 mm) -0.9%
315/25R19 25.2″ (641 mm) -0.9%
305/30R18 25.2″ (641 mm) -0.9%
225/35R19 25.2″ (641 mm) -0.9%
265/30R19 25.3″ (643 mm) -0.6%
265/35R18 25.3″ (643 mm) -0.6%
155/60R18 25.3″ (643 mm) -0.6%
225/30R20 25.4″ (644 mm) -0.5%
145/65R18 25.4″ (645 mm) -0.3%
115/70R19 25.4″ (645 mm) -0.3%
235/40R18 25.4″ (645 mm) -0.3%
135/60R19 25.4″ (645 mm) -0.3%
275/25R20 25.4″ (646 mm) -0.2%
135/70R18 25.5″ (647 mm) 0%
235/35R19 25.5″ (647 mm) 0%
275/35R18 25.6″ (649 mm) 0.3%
275/30R19 25.6″ (649 mm) 0.3%
285/25R20 25.6″ (650 mm) 0.5%
235/30R20 25.6″ (650 mm) 0.5%
215/45R18 25.6″ (651 mm) 0.6%
335/25R19 25.6″ (651 mm) 0.6%
245/40R18 25.7″ (653 mm) 0.9%
245/35R19 25.8″ (655 mm) 1.2%
285/30R19 25.8″ (655 mm) 1.2%
215/40R19 25.8″ (655 mm) 1.2%
295/25R20 25.8″ (656 mm) 1.4%
245/30R20 25.8″ (656 mm) 1.4%
285/35R18 25.9″ (657 mm) 1.5%
125/70R19 25.9″ (659 mm) 1.9%
225/45R18 25.9″ (659 mm) 1.9%
335/30R18 25.9″ (659 mm) 1.9%
305/25R20 26″ (660 mm) 2%
145/70R18 26″ (661 mm) 2.2%
185/55R18 26″ (661 mm) 2.2%
295/30R19 26″ (661 mm) 2.2%
255/35R19 26″ (661 mm) 2.2%
355/25R19 26″ (661 mm) 2.2%
255/40R18 26″ (661 mm) 2.2%
255/30R20 26.1″ (662 mm) 2.3%
295/35R18 26.1″ (663 mm) 2.5%
225/40R19 26.1″ (663 mm) 2.5%
205/50R18 26.1″ (663 mm) 2.5%
345/30R18 26.2″ (665 mm) 2.8%
225/35R20 26.2″ (666 mm) 2.9%
315/25R20 26.2″ (666 mm) 2.9%

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