P315/40R18 in inches

How tall is a P315 40R18 tire?

When converted to inches, the equivalent of a P315/40R18 tire size is 28x12.4R18. It means that:

  • height overall (or diameter) is 28 inches
  • tread width is 12.4 inches
  • wheel diameter is 18 inches

Learn more

P315/40R18 tire size in inches
P315/40R18 tire size chart

P315/40R18 tire size in inches

P315/40R18 Height / overall diameter: 28 inches
Height / overall diameter
28 inches
P315/40R18 Tread width: 12.4 inches
Tread width
12.4 inches
P315/40R18 Sidewall: 5 inches
Sidewall
5 inches
P315/40R18 Wheel diameter: 18 inches
Wheel diameter
18 inches
P315/40R18 Circumference: 87.9 inches
Circumference
87.9 inches
P315/40R18 Revolutions: 721 per mile
Revolutions
721 per mile

P315/40R18 — what does it mean?

  • P means "passenger car"
  • 315 stands for tread width in millimeters
  • 40 is an aspect ration between the tread width and the sidewall in percents
  • R means that the tire has a radial construction
  • 18 is a wheel diameter (or rim) in inches

P315/40R18 tire code
P315/40R18 tire code

How to convert P315 40R18 to inches?

First of all, we need to divide 315 mm (width) by 25.4 (mm to inch conversion), which will give us a width of 12.4″. Then, 40% of the 12.4″ will result in 5″ sidewall.

To get the total height or tire diameter, we need to sum the 18″ rim diameter with two of the sidewall heights. It will result in a 28″ total tire diameter (or height).

For your convenience, below is a table for P315/40R18 conversion to inches:

Inches Metric
Overall diameter (height) 28″ 711 mm
Tread width 12.4″ 315 mm
Wheel diameter 18″ 711 mm
Sidewall height 5″ 126 mm
Circumference 87.9″ 2233 mm
Revolutions 721 / ml 448 / km

Alternatives to a P315/40R18 tire

If you're looking to upsize your P315 40R18 tires, try to stay within 3% deviation of an overall diameter for safety reasons.

Tire Tire diameter Width Wheel Size
295/45R18 28.4″ 0.35% 11.6″ 18″
225/60R18 28.6″ 0.52% 8.9″ 18″
245/55R18 28.6″ 0.52% 9.6″ 18″
145/85R18 27.6″ -0.35% 5.7″ 18″
155/80R18 27.8″ -0.18% 6.1″ 18″
155/85R18 28.4″ 0.35% 6.1″ 18″
205/60R18 27.6″ -0.35% 8.1″ 18″
215/55R18 27.2″ -0.71% 8.5″ 18″
225/55R18 27.8″ -0.18% 8.9″ 18″
235/50R18 27.2″ -0.71% 9.3″ 18″