Understanding MOA


If you are reading this article, you enjoy reading about guns. That means you have probably read articles that refer to MOA when discussing accuracy, which includes comments like “this gun shoots sub-MOA groups.”

Everyone seems to agree that is a good thing. Why it is a good thing might be unclear to some folks. Understanding MOA, how it is calculated, and what it means in terms of accuracy will make references to it much more meaningful.

What is MOA?

MOA stands for Minute of Angle. It’s a measure of angle as opposed to a linear measurement on a straight line. This makes sense if you think of your target as a circle, which, of course, it is. When we shoot at a target, we aim at a center point on the target. Our success is measured by how tightly all our shots group on the center bullseye. For example, you put five shots into a 2″ group or circle at 100 yards.

That’s fine for giving us a rough measure of our accuracy, but it doesn’t help us much in knowing how many clicks to adjust an optic to get a smaller circle. For that, we need to use MOA, which is why scopes adjust in MOA per click.

Calculating MOA

You have probably noticed that you see less of an object that is close than you do of the same object when it is farther away. That’s because the human eye sees objects at a visual angle. You can read the scientific details here, but for our purposes, it’s enough to understand that we see things as parts of an angle. 

The rings on a target form a 360° circle, and bullet impacts in the circle form a cone. For example, you shoot two shots at the target and hit it once above the bullseye and once to the left of the bullseye. If you draw a line from each bullet hole to the center of the bullseye, those lines would form a cone. Each of those lines would also form the sides of an angle. Measuring that angle would tell you how many degrees it represents in the 360° circle. Because we have angular vision and because bullets strike the target in a cone, we use MOA rather than inches to adjust the bullet strike.

MOA is a Very Small Measurement

We know that a minute measures 1/60th of an hour, but it also measures 1/60th of a degree. Minutes are used to break degrees into 60 parts in longitude and latitude measurements, and seconds are used to break minutes into 60 smaller parts. For example, the latitude and longitude of the Washington Monument is latitude 38° 53′ (minutes) 22″ (seconds) N, longitude 77° 2′ (minutes) 7″ (seconds) W. The system is easy to relate to because everyone is familiar with minutes.

In determining MOA, a minute is 1/60th of a degree. So, 1 MOA = 1/60th of a degree in that 360° circle around the bullseye. That’s an insignificant measurement at 1 inch from the muzzle, but it gets more meaningful at longer ranges.

We use MOA rather than a full degree because a full degree would be too large to do us any good. An MOA is 1″ at 100 yards, but a full degree would be 60″ at 100 yards. If you know what an MOA is and how it relates to your bullet strikes over range, it isn’t difficult to figure it out for any range.

Converting Inches to MOA

We measure how far we miss the bullseye by inches, and scopes adjust in MOA. So, we have to be able to convert the inches to MOA to make adjustments. If you know what range you are shooting at and how far you are consistently missing, that isn’t difficult. The key word here is consistently. MOA calculations only matter if you are using proper marksmanship techniques.

Given that 1″ is 1 MOA at 100 yards, the math is simple to determine what it would be at any range. Simply take inches divided by yards times 100 (inches/yards X 100). So if you are off by 3″ at 200 yards it would be: (3″/200 yards) X 100 = 1.5 MOA. If your scope or red dot adjustment is .5 MOA per click, it would be three clicks in the appropriate direction. It will work for any number of inches at any range. 

Converting MOA to Inches

To convert MOA to inches, simply reverse the formula. Range times MOA divided by 100 (Range X MOA/100). Using the same example as above, it would be 200 yards times 1.5 MOA divided by 100 = 3″. In this case, each .5 MOA click of adjustment should change the bullet strike by 1″.

One MOA Is One MOA

A one MOA adjustment is a one MOA adjustment at 100 yards or 1000 yards. But that one MOA adjustment will change the bullet strike by 1″ at 100 yards and 10″ at 1000 yards. As you already know, a small change at a close range will be a large change at a long range.

MOA is a Rounded Number

It may seem counter-intuitive, but we use rounded MOA to make precise adjustments to our scopes. But in practice, the decimal places we round off the exact MOA at any given range won’t make any difference in measuring or adjusting the strike of the bullet. Since one MOA is 1/60th of a degree, the actual effect of the decimal places is infinitesimal.

Using MOA to Zero an Optic

When I was a youngster sighting in my .30-06 rifle before deer season, I’d never heard of MOA, and neither had anyone else hunting with me. I would get a box of shells, guestimate 100 yards, and start shooting. I would take a shot and see where it struck, then adjust a few clicks and take another shot. After a few rounds, I would be good to go. It was all trial and error. Using MOA, we can get a good zero with a couple of shots.

Zeroing a Scope

Since MOA is a measure of angle, not a linear distance, you adjust in both elevation and windage. A number of clicks up or down, and a number of clicks left or right. You are moving the strike around on an X and Y axis with the center of the bullseye at the point where the X and Y lines cross.

How Many Clicks Equal an MOA

Look at any listing for a scope, and you will see an entry telling you what each click of the adjustment knob equals in MOA. Most scopes are set up so that one click equals ¼ or .25 MOA or ½ or .5 MOA. The smaller the increment, the more precise your adjustments will be. A ¼ MOA per click adjustment will give you more precision than a ½ MOA per click scope adjustment.

Adjusting to Zero

Using MOA makes it relatively easy to zero your scope. Ideally, you will be shooting from a bench, and your rifle will be settled into a firm rest to minimize movement during the shot to remove unwanted variables. The idea is to shoot from a stable platform so you can remove as much error as possible from your shots.

Shoot a group of three shots and go see where they hit. Let’s say your group is 1″ high and 2″ to the left. If you are zeroing at 100 yards, your scope is shooting 1 MOA high and 2 MOA to the left. If your scope adjustment is ¼ MOA per click, you would have to turn your elevation adjustment down four clicks and your windage adjustment to the right eight clicks.

MOA and Accuracy

The other use of MOA is to measure the accuracy of a firearm. This is where you will hear or read that a handgun or rifle can achieve ‘X’ MOA groups. When using MOA to measure accuracy, just use the formula to convert inches into MOA at a known distance. Measure the spread of your group in inches and convert it to MOA.

MOA And Red Dots

MOA is used in two ways with red dots. The first is to adjust the strike as with any other optic. The sight specs will include adjustment type and adjustment click value. The type will say ‘MOA,’ and the adjustment click value will tell you the MOA value for each click.

Adjusting a red dot is like adjusting a scope. Most red dots are set for either ½ or 1 MOA per click. Since you are working with much shorter ranges, that is plenty of precision. The most common distance for zeroing a red dot is 50 yards.  

The process is the same as for a scope. Shoot your group, measure your spread from the aiming point, determine how many MOA you need to adjust, and turn the appropriate number of clicks.

The Size of the Dot

The other application of MOA for red dots is the size of the dot, and it is generally listed under reticle. MOA sizes for reticles refer to the size of the dot at 100 yards. The most common reticle dots are 2 MOA, meaning the dot will be 2″ at 100 yards. That’s perfect for a handgun since larger dots are easier to pick up quickly. Some tactical sights for CQB have dots as large as 8 MOA. 

But as the range increases, so does the size of the dot relative to the target. A 2 MOA dot will be 4″ at 200 yards, 6″ at 300 yards, and so on. That means if you are using a red dot on a rifle or carbine, you will probably want to go for a small MOA dot.

Some sights have reticles consisting of a smaller MOA dot surrounded by a large MOA circle. These circles are commonly 65 MOA. There is no ‘best’ MOA size for a dot reticle. It is entirely a matter of preference.

Red Dot summary:

  • A 1 MOA dot is 1 inch at 100 yards
  • 2 MOA is a common reticle size
  • The longer the range, the more of the target will be covered by the dot
  • A smaller MOA dot is preferable for longer ranges
  • A larger MOA is preferable for handguns and CQB at shorter ranges

Using Mils

Mils is the same kind of system as MOA, but it is measured on a metric scale using centimeters. Precision scopes most often have Mil reticles, while hunting scopes mostly use MOA. The military uses Mils because it is NATO standard. If you are using a scope set up in Mils, you’re better off using meters for range rather than yards. That way, everything is working at powers of 10 to keep the math simple.

One Mil is a consistent measure no matter the range, just like MOA. A 360-degree circle has 6400 Mils. At 100 meters one Mil = 10cm, at 200 meters 1 Mil = 20cm, and so on. Most scopes that use a Mil reticle are set up at .1 Mil per click of adjustment. That’s 1/10th of a Mil, so at 100 yards, one click of adjustment would move the strike point 1cm.

Converting Mils to MOA

Converting between the two systems takes a little getting used to. There are lots of apps for your smartphone to do the math for you. In general, the conversions are as follows:

  • 91.4 meters = 100 yards
  • 2.54cm = 1 inch
  • 10cm = 3.9 inches (10cm/2.54 = 3.9”)

Although the numbers are different between Mils and MOA, the practical application is the same. Shoot a group, measure how far off you are from your point of aim, and make the appropriate adjustments to your scope.

It’s Not Magic or Rocket Science

There’s nothing mysterious or highly technical about MOA and how to use it. Like your rifle and optic, it is a tool to accomplish the goal of hitting what you aim at. Learning to use it will save you time, money, and aggravation.

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