Standard Handgun shooting distance.
How can you evauate accuracy like this?
You cannot. Your group size has to be compared to some standard.
When I was a teenager, there were defacto accepted standards at which group-sizes could be compared for handgun shooting based on "Bullseye", off-hand, single-action, shooting (one handed, unsupported). The course of fire was usually 50 yards for slow-fire, and 25 yards for rapid fire for center-fire handguns (at that time .38 revolver and .45 automatics were pretty much standard). When one would talk about group size, it was assumed that it was a five-shot group.
http://en.wikipedia.org/wiki/Bullseye_(shooting_competition)
In those days, after seeing and measuring enough groups, when someone would announce the size of the group he had just shot, one would know how good it was relative to those standards.
Nowadays, tradition has given way to forging ahead without spending the time to learn from what has been the tradtion before. That coupled with the demise of off-hand "Bullseye" shooting in favor of the more relevant-to-combat and self-defense practice (after all, no one today would consider one-handed shooting to be appropriate for combat/defensive shooting), that encourage double-tap, on multiple targets, the distances and the course of fire has changed.
Therefore, no standard distance except as prescribed for a particular event. But if you want to compare how good a group you can shoot compared to someone else, use five shots at 25 yards, measured center to center. And for gosh sake, do not, never, shoot three shots and call that your group...it alienates we old people who cannot get beyond traditional five-shot groups. Darn kids these days!