The gear I have has a diameter of 9.4mm and 15 teeth. According to this calculator, the pitch should be 0.55 MOD or 45.94p.

The next thing I wanted to do was find the steps per millimeter this setup. Using this formula (near top, scroll down a little), I found that my setup would have 388 steps per mm, which seems REALLY high.

I think I messed up the pitch calculation. In the example used on the second link with the formula, the pitch for the belt was 2. Because I am using a recycled belt, there is no datasheet I can use to lookup anything.

I just realized there is a part number on it: s2m806ug
When I google it, the belt does come up, but only links to buy it, no datasheet (and most of it is in spanish )

The pitch is the distance, center to center, of two adjacent teeth on the belt. For a drive gear, measure from the center of one valley to the next. That is where the belt will fit.

If diameter is 9.4mm circumference is 9.4 * Pi = 29.531 / 15 teeth = 1.97mm, I’d call it 2mm so one rev = 30mm, steps per mm would be steps / rev / 30. For a 200 step motor that would be 200 / 30 = 6 2/3 steps / mm or 0.15 mm / step.
Does that sound right?

I used a caliper, which is probably the worst way of doing this, and got a little under 2mm, so I guess I'll round to 2 mm for now? I will finish the build and experiment to see if the calculation is accurate.

electricviolin:
I used a caliper, which is probably the worst way of doing this, and got a little under 2mm, so I guess I'll round to 2 mm for now? I will finish the build and experiment to see if the calculation is accurate.

Why do you think that is so? That is probably what I would have done. This is not rocket science.

To get better tooth pitch accuracy try measuring the distance on 10 (or more) teeth and divide the result down.

All of this seems irrelevant to me as the teeth on the belt are only there to prevent belt slip. It does not matter if the tooth pitch is 1,2 or 3mm as long as the sprocket is using the same pitch. The important part is the sprockets effective diameters.

Okay sounds good! Given this information, I found that I will get 24 steps per millimeter (This is for a 3D printer build)... I am not sure if that is high enough, but I will try and see what happens.