True Mil Dot is 100mm at 100m. this the reduces in proportion i.e. 50mm at 50m 25mm at 25m etc. etc. Th scope maker should state the mag at which mil dots are 'true'. On some makes including Bushnells the mag at which the Mil Dot is 'true' is marked in a different colour.
Make every shot count
Steyr Hunting 5 Scott Lupold 3-9x33EFR(for LSR )
FWB P70/Bushnell 6500 4-30x50T
SteyrLG110/Bushnell 6500 5-30x50
Steyr LG 100 FT Bush elliot 8-32x40