Excerpt from my Grbl-HAL firmware as compiled;
// STEPS_PER_MM is (Steps for 1 rotation * microsteps) / mm achieved per rotation
// Typical GT2 belt is 2mm per tooth, a 20-tooth ‘gear’ on stepper thus 40mm/rotation
// Thus (200 * 8) / 40 = 40 for 1.8deg stepper, 8 microsteps, 20-tooth on GT2
#define DEFAULT_X_STEPS_PER_MM 40.0f //250.0f
#define DEFAULT_Y_STEPS_PER_MM 40.0f //250.0f
#define DEFAULT_Z_STEPS_PER_MM 320.0f //250.0f
My actual, just downloaded $$ settings. Note that as my machine has a permanent A-Rotary axis, I have $103 defined, and similarly $113, $123 and $133. I also have the HDZ upgrade, so my Z settings may look different to yours.
$100=40.000 (X-axis travel resolution, step/mm)
$101=40.000 (Y-axis travel resolution, step/mm)
$102=320.000 (Z-axis travel resolution, step/mm)
$103=26.667
$110=4000.000 (X-axis maximum rate, mm/min)
$111=4000.000 (Y-axis maximum rate, mm/min)
$112=660.000 (Z-axis maximum rate, mm/min)
$113=6480.000
$120=350.000 (X-axis acceleration, mm/sec^2)
$121=350.000 (Y-axis acceleration, mm/sec^2)
$122=80.000 (Z-axis acceleration, mm/sec^2)
$123=300.000
$130=878.000 (X-axis maximum travel, mm)
$131=430.000 (Y-axis maximum travel, mm)
$132=140.000 (Z-axis maximum travel, mm)
$133=1440.000