I have made the dumb purchase locally of a 20T pulley set and GT2 belt. Unfortunately I have to wait for 2 weeks until the new 16T pulleys arrive that I ordered tonight.

What line do I adjust to compensate for the 20T pulleys? What will the new value be please.

I assume this will be the reason I am getting 12.5mm instead of 10mm when I send 10mm command from repetier?

I assume this formula is correct?

(steps * microstepping) / (teeth * pitch)

One revolution of a 1.8° stepper is 200 steps * 16 = 3200 steps/revolution.

For GT2 (2mm) belt and a 20 tooth pulley 1 revolution = 2 * 20 = 40 mm/revolution.

3200 steps/revolution * 1 revolution/40 mm = 80 steps/mm.