Tools › Group Size
Group Size Calculator
Two methods. Drop in extreme spread from your calipers, or paste a list of shot coordinates for max center-to-center, mean radius, and MOA at distance.
What These Words Mean
- Group
- The cluster of bullet holes you put on a target by aiming at the same spot multiple times. Smaller is better.
- Extreme spread
- The distance between the two farthest holes in your group. Easy to measure but a single bad shot ruins it.
- Center to center (CTC)
- Same as extreme spread but measured from the center of one hole to the center of the other (not edge to edge). The standard way shooters report group size.
- Mean radius
- The average distance from each shot to the middle of the group. Less affected by one weird shot. What competitive shooters actually trust.
- MOA
- An angle that opens up about 1 inch wider every 100 yards. A “1 MOA group” is about 1 inch at 100 yards, or 2 inches at 200 yards.
Method 1: Extreme Spread
You shot a group, then measured the two farthest holes edge-to-edge with calipers. Type that measurement here. We subtract one bullet diameter so the result is center-to-center, the way most shooters report it.
Method 2: Shot Coordinates
If you measured the position of each shot (for example with a target-scoring app), paste them here as x,y pairs, one shot per line. We compute every group statistic worth knowing in one shot.
What These Numbers Mean
Center-to-center (ctc). The distance between the two farthest bullet holes measured from center to center. The standard "group size" most shooters report.
Mean radius. The average distance from each shot to the group's centroid. Less sensitive to a single flyer than max ctc, which is why competitive shooters and statisticians prefer it for load comparison.
Avg-to-center. Same idea as mean radius, named differently in some load-development circles. Reported here for completeness.
Disclaimer. Educational. Not load data. Always verify against a current published reloading manual.