The so-called "spread" depends on several factors. the gauge of the shotgun and barrel length. example: an illegal saw-off shotgun, will give a greater spread pattern, than the original length.

I recommend you to the following site... they have a pic on there that will give you an idea of what a standard spread and close up perferation looks like...it also has other useful info. http://www.firearmsid.com/A_distshotpatt.htm

At one time I owned a Mossberg 500 20 gauge shotgun for home defense. I chose this particular weapon specifically because it is sometimes known as an "Apartment Gun". This weapon had a 18 1/4 inch barrel, and a pistol grip. As such, it was legal as the minimum barrel length is 18 inches. With the shortened barrel and the pistol grip, it was easily maneuverable in a small area such as a hallway or small room. With a medium load birdshot shell, you didn't need to worry about a round going through a wall and unintentionally wounding or killing someone in the next room. When I went shopping for the weapon, I went with a friend who was a federal police officer. I intended to purchase a semi-automatic shotgun, but he convinced me to go with the pump for two reasons. First, a pump doesn't jam, and second, the sound of chambering a round with a pump may act as a deterrent to a home invader. As my friend stated, "I have been on both sides of a shotgun when I heard that sound, and it definitely makes you stop and think about what your next move is going to be." Now that I have gone on a complete tangent, your original question asked about the spread of a home defense shotgun. Since I consider the gun I had as a good home defense gun, I will give you my experience with it. Keep in mind, that this is about the minimum length barrel you can have, with no choke. The spread on my gun was approximately 4 inches at a distance of 10 feet. Again, this was using birdshot (number 8 I think...been a few years) fired into a paper target on a range. The spread at 5 feet was less than 3 inches. It opened up to around 8 inches at 15 feet, which is about the maximum distance you are likely to fire a shotgun from in a home defense situation.