Each bearing has an inside diameter, outside diameter and width diameter in that order. Most bearings are metric in size, but can also be imperial. On our site, each bearing shows its principal dimensions.
d = Inside diameter
D = Outside diameter
B/T = Width diameter
You can search for a bearing entering this information on the home page in the boxes provided.
Once you have identified the bearing's code some bearings come complete with seals or shields. This is known as the suffix in the bearings reference.