1 mil in a scope reticle is the distance from the center of one dot to the center of the next dot.
Set your scope at 10x power. View the target through the scope. Place the center of the dot against one edge of the target and measure to the opposite of the target.
Once the target has been measured in mils, use the formula below to calculate the target distance:
Height or Width of Target in Meters x 1000 = Range in Meters =Range in Meters
Height or Width of Target in Mils = (1M=1.0936 Yards)=(1M=1.0936 Yards)
The Mil-Dot Range Estimate Reference Chart provides most used estimates for reference.