The arithmetic to calculate diameter of your tire.
For example:
Your tire is written with P215/70R16,A=215 B=70 C=16
Your tire's diameter=A*B/500+C*2.54=215*70/500+16*2.54=70.74CM
Size S (14 inch) fit for diameter 60-69cm(24"-27")
Size M (15 inch) fit for diameter 70-75cm(28" 29")
Size L (16 inch) fit for diameter 76-79cm(30"-31")
Size XL (17 inch) fit for diameter 80-83cm (32")
Than you need to buy 15 inch one.
Specifications
Including: 1pc spare tire cover
Packing:Environmental Packing
Material: PVC leather
Install:Need to adjust edage