To read tire size, you need to look at the sidewall of your tire and find a sequence of letters and numbers that usually starts with "P". This sequence tells you the width, aspect ratio, construction, wheel diameter, load index and speed rating of your tire.
P means it is a passenger car tire.
For example, if your tire size is P225/65R17 95H:
225 means it has a width of 225 millimeters.
65 means it has an aspect ratio of 65%, which is the height of the sidewall divided by the width.
R means it has a radial construction.
17 means it fits on a wheel with a diameter of 17 inches.
95 means it has a load index of 95, which indicates how much weight it can carry.
H means it has a speed rating of H, which indicates how fast it can go safely.