Minute of angle: the one unit every rifleman needs

A minute of angle (MOA) is one sixtieth of a degree — an angular measure, not a distance. Because angles scale with range, one MOA is about 1.05 inches at 100 yards, about 2.1 at 200, about 5.2 at 500. That single idea, small angle growing into linear inches, is the whole of MOA. Everything else is arithmetic.

The unit exists because rifle accuracy is angular. A rifle that prints one-inch groups at 100 yards also prints four-inch groups at 400; the rifle has not got worse, you have moved back. Measuring in inches would punish distance. Measured in MOA, the rifle’s number stays the same wherever you shoot it.

What one MOA is worth at distance

There are 360 degrees in a circle and 60 minutes in a degree, so a circle contains 21,600 minutes of angle. The inches follow from that alone: at any distance, multiply the range in yards by 1.047 and divide by 100.

This is why accuracy claims are quoted in MOA. A “one-MOA rifle” shoots about a one-inch group at 100 yards, two inches at 200, five at 500. Most hunting rifles with factory ammunition live between 1.5 and 3 MOA; a half-MOA rifle is match equipment with match ammunition behind it. When someone quotes group size in inches without the distance, the number means nothing.

What a click is worth

Scope turrets are cut in angular steps. The common American convention is a quarter-MOA click: each detent moves the point of impact 0.25 inches at 100 yards, 0.5 at 200, 2.5 at 500. Some target scopes use eighth-MOA clicks. Metric scopes move 0.1 mradian per click, which we come to below. Your scope’s manual states which one you own, and guessing is how people end up three times further from zero than they started.

The conversion from a miss to a correction has two steps, and neither involves trigonometry:

1. Work out the error in MOA. Divide the miss in inches by the range in hundreds of yards. Six inches low at 200 yards is 6 ÷ 2 = 3 MOA. Nine inches left at 300 is 9 ÷ 3 = 3 MOA.
2. Convert to clicks. Divide by the click value. At quarter-MOA clicks, 3 MOA is 12 clicks. That is the entire method.

Two habits make the arithmetic hold up on a live range. Adjust in whole clicks and confirm with a three-shot group, never a single round — one hole tells you nothing about where the group center went. And make corrections at the distance you measured the miss: an angular fix that closes three inches at 100 yards closes twelve at 400, which is the point of the unit, and also how people overshoot when they forget it.

Mradians, briefly

A milliradian (mrad or mil) is the metric cousin: one thousandth of a radian, with a full circle holding about 6,283 of them. At 100 yards, one mrad is 3.6 inches; a 0.1 mrad click is 0.36 inches. One mrad is roughly 3.44 MOA, so the two systems are interchangeable with a factor — the mistake is mixing them mid-calculation.

Mradians suit people who like base-10 steps and rangefinder-style arithmetic; MOA suits shooters raised on quarter-inch-at-a-hundred intuition. Neither is more accurate. Pick one, keep your turret, your reticle and your ballistic data in it, and convert only on paper. If your scope has a first-focal-plane reticle, its subtensions hold at any magnification; a second-focal-plane reticle only measures correctly at the magnification it was calibrated for.

MOA also handles the occasional ranging check. A target of known size that spans a measured number of MOA sits at roughly (size in inches × 95.5) ÷ MOA yards — an 18-inch plate covering two MOA is about 860 yards. A laser makes this theoretical, but the same relationship is what tells you whether the laser is reading what you think it is.

A working order of operations

• Identify your clicks. Read the turret markings or the manual: quarter-MOA, eighth-MOA, or 0.1 mrad. Everything depends on this one fact.
• Zero with a group of at least three shots at a stated distance, using the load you intend to shoot. Changing bullet weight moves the group, and so does a pressure change — a +P carry load is not automatically zeroed to your standard-pressure practice ammunition. A zero is a zero for one load.
• Convert the miss with inches ÷ hundreds of yards = MOA, then MOA ÷ click value = clicks.
• Adjust, then re-shoot the group. Never chase a single hole, and never adjust twice before confirming once.
• Record the dope. Once the rifle is zeroed, the same arithmetic reads backwards from a drop chart: if a load needs eight MOA from a 100-yard zero at 400, that is 32 quarter-MOA clicks, or written down, one number you will not be calculating in the wind.

MOA is not a marksman’s secret; it is a protractor in nicer clothes. Learn what one minute is worth at the distance you shoot, and the scope stops being a mysterious instrument and becomes what it always was — a dial that moves an angular inch at a time.