Wheel size varies by bike type. (Common Widths: 700c, 29”, 28”, 27.5”, 26”, 24" and 20")
Road bikes and urban bikes with narrower tires are normally called 700c and Mountain bikes are called 29" (29er) or 27.5" or 26". Often, this is noted on your tire’s sidewall. Sometimes you will see one set of sizing numbers on a tire, or two or event three. As long as your tire numbers match our fender guide you will buy the right fender.
A tire size you might see on a mountain bike:
29 x 2.35 indicates a tire with a 29" wheel size and a 2.35" tire width.
A tire size you might see on a road bike:
700x25c indicates a tire with a 700mm wheel size and a 25mm width.