Minutes of angle and milliradians describe angles, not fixed target sizes. Because an angle subtends more distance as range increases, either unit can describe group size, sight adjustment, reticle holds, target dimensions, and corrections at any distance.
Minute of angle
One minute of angle (MOA) is 1/60 of one degree. It spans approximately 1.047 inches at 100 yards, 2.094 inches at 200 yards, and 10.47 inches at 1,000 yards. For quick field estimates, shooters often use one inch per 100 yards, but the approximation accumulates error as distance grows.
Milliradians
One milliradian (mil or mrad) is 1/1,000 of a radian. It spans 0.1 meter at 100 meters, 0.5 meter at 500 meters, and one meter at 1,000 meters. In imperial units, one mil spans 3.6 inches at 100 yards.
One mil equals approximately 3.438 MOA. The systems are different scales for the same kind of angular relationship.
Measuring a group
Measure the extreme spread from the centers of the two farthest impacts. A convenient method is to measure outside edge to outside edge and subtract one bullet diameter. Then divide the group size by the distance represented by one unit at that range.
- A 2.094-inch group at 200 yards is approximately 1 MOA.
- A 7.2-inch group at 200 yards is approximately 1 mil.
- A 5-centimeter group at 100 meters is 0.5 mil.
Group size describes the combined result of firearm, ammunition, shooter, position, environment, and sample size. A single small group does not establish the long-term precision of the system.
Using optic adjustments
Turrets are commonly marked in fractions of MOA or mils. A 0.25-MOA click moves the point of impact about 0.26 inch at 100 yards. A 0.1-mil click moves it one centimeter at 100 meters. Confirm the actual adjustment value in the optic manual and verify tracking rather than relying solely on the marking.
Keep the reticle and correction system consistent
Corrections are simplest when the reticle and turrets use the same unit. If a miss measures 0.6 mil in a mil reticle, dial or hold 0.6 mil. Converting between mils and MOA adds time and opportunities for error.
Angular size is not probability
A stated “one-MOA rifle” does not guarantee every shot will land within a one-inch circle at 100 yards. Dispersion is statistical, and the probability of a hit also depends on zero, wind, range estimation, ammunition, shooter performance, and target size.
Use the units marked on the actual optic, current manufacturer documentation, and confirmed live-fire data. Related: Optics and Red Dots Hub.
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