315/40R21 in inches

How tall is a 315 40R21 tire?

When converted to inches, the equivalent of a 315/40R21 tire size is 31x12.4R21. It means that:

  • height overall (or diameter) is 31 inches
  • tread width is 12.4 inches
  • wheel diameter is 21 inches

Learn more

315/40R21 tire size in inches
315/40R21 tire size chart

315/40R21 tire size in inches

315/40R21 Height / overall diameter: 31 inches
Height / overall diameter
31 inches
315/40R21 Tread width: 12.4 inches
Tread width
12.4 inches
315/40R21 Sidewall: 5 inches
Sidewall
5 inches
315/40R21 Wheel diameter: 21 inches
Wheel diameter
21 inches
315/40R21 Circumference: 97.3 inches
Circumference
97.3 inches
315/40R21 Revolutions: 652 per mile
Revolutions
652 per mile

315/40R21 — what does it mean?

  • 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
  • 21 is a wheel diameter (or rim) in inches

315/40R21 tire code
315/40R21 tire code

How to convert 315 40R21 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 21″ rim diameter with two of the sidewall heights. It will result in a 31″ total tire diameter (or height).

For your convenience, below is a table for 315/40R21 conversion to inches:

Inches Metric
Overall diameter (height) 31″ 787 mm
Tread width 12.4″ 315 mm
Wheel diameter 21″ 787 mm
Sidewall height 5″ 126 mm
Circumference 97.3″ 2471 mm
Revolutions 652 / ml 405 / km

Alternatives to a 315/40R21 tire

If you're looking to upsize your 315 40R21 tires, try to stay within 3% deviation of an overall diameter for safety reasons.

Tire Tire diameter Width Wheel Size
255/50R21 31″ 0% 10″ 21″
265/45R21 30.4″ -0.48% 10.4″ 21″
275/45R21 30.8″ -0.16% 10.8″ 21″
275/50R21 31.8″ 0.66% 10.8″ 21″
285/45R21 31″ 0% 11.2″ 21″
295/40R21 30.2″ -0.64% 11.6″ 21″
325/40R21 31.2″ 0.16% 12.8″ 21″
P265/45R21 30.4″ -0.48% 10.4″ 21″
P295/40R21 30.2″ -0.64% 11.6″ 21″