How many millimeters are in one revolution of my bike's wheel?

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ftbtef

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I got a bike computer and it wants to know:
"the correct, 4-digit, wheel value based on the size of your tire. The wheel value is the distance in millimeters per one revolution of the wheel."

I'm not sure how exactly I should calculate this. My bike wheel is 17.5". I also am not sure if that refers to diameter or radius. Any help?
Also, the manual tells me a 20 inch tire=1596mm per one revolution, 22=1759, 24=1916, 26=2073, and 27=2124. These measurements are for road bikes, which is what I have.
 
Don't calculate it, measure it. On your garage floor or sidewalk, rotate the front wheel so the air valve is at the very bottom. Put a pencil or chalk mark on the concrete next to the valve. Then, while pushing down on the handlebars, walk the bike forward until the valve is again at bottom. Make another mark next to the valve. Measure the distance between the marks.

You need to measure it to get the most accurate distance and speed because there is some circumference variation in different brands and models of tire even when they all fit on the same size wheel.
 
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