MOA is generally associated with the extreme spread of a group, center to center of the furthest spaced holes. So if that was how you came up with a 3 1/2”  radius, your group would be +/- 7 MOA.

There is another method of measuring groups called “Mean Radius” which is basically the average distance of all shots from the center of the group. Not from the point of aim.
Article on mean radius
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Here’s a photo of a target measured both ways 

If it’s just a quick measurement, a reference point, I just measure inside edge of one hole to the outside of the other. That will be very close to the center to center measurement. To me it’s easier than subtracting bullet diameter. The holes aren’t bullet diameter any way, so by subtracting bullet diameter your group comes out smaller than it actually is.

A 2” group at 100 yards is basically 2 MOA. 
If you divide group size by 100, 2/100=0.02 and you pull 2” group out your wallet after telling everyone at the club you shot a .02 MOA group, you’re buying everyone drinks.

Divide distance to target by 100, then divide group size by that.
100/100=1 2/1 =2 MOA 
500/100=5 2/5=0.4 MOA 
1000/100=10 2/10=0.2 MOA 

Hope that’s a good start.

The way that it is done in CBA match shooting, is to measure the outside to out side of the leaded edge of the holes. Then you subtract the groove size of the rifle barrel, for group size.

That is the basic way it is done to set CBA records. Many ASSRA scorers do it the same way. There are other ways but, that is the most common.

To be clear, 1" is not MOA. 1.047 is MOA at 100 yards.

MOA is a measurement of degrees and is 1/3600 of a circle. It is expressed such as this:

Example 1° 1'

The measurement, is how much that angle diverges. Inch and minute, have nothing in common but, that they are .047 different at 100 yards but, differ more as yardage increases.

''Now I think I’ll have that drink. 👍👍👍''

You and me, both. 
I just say the size in inches and let somebody else do the senseless mathematical gyrations. I'm not navigating a route thru the galaxy, I'm measuring a series of holes in a target for crying out loud. 

Babydriver wrote on Mar 24^th, 2025 at 10:46pm:


I've found it's often tough to be precise by measuring what appears to be bullet center of a hole. So I measure outside edges at the furthest point on each edge and deduct the diameter of the bullet from that measurement.

If that is a scorpion- at the size of it even the smallest of ours would whip it. I once saw a scorpion dumped from a miner's boot in the middle of the state that was about three inches-  a lousy group to shoot, but one helluva scorpion!
I want to see the moose also

not bad. here's a big ol' attaboy
If you aren't animals exclusively, do you do portraits? maybe family or friends?