On each tyre's sidewall there is this tyre size
Due to the fact that the tyres are provided with the most important parameters on the sidewall, they are the subject of ECE-R 30.
The first number given in this descritpion is the width e.g.: 195 This value is given in milimetres and is meaured between the longest outer and inner sidewall point fitted to the right tyre. Difference of 10 milimetres on the width means that those are two different tyres. Although this value can differ a bit from the real value, it is still unnoticable and depends on the manufacturer.
Profile is given at a second place in the mentioned markings. Tyre 195/65 R 15 has a profile 65, which is 65% of 195 milimetres of width. In this particular case the tyre is 126,75 milimetres high.There are low profile tyres of 40, 45 and 55 and full profile, which do not have the proper profile markings as the profile is 80.
Tyre's radial construction means that the pile cords ar at 90 degrees to the bead. In the tyre description the radial build of a tyre is indicated by the R. In the tyre195/65 R15 carcas is radiating from the centre of the wheel. 98% of tyres sold are radial tyres.
The number 15 - indicates the size of the wheel on which the tyre is to be placed. Manufacturers give the size in inches.