In "The Walking Dead" and other zombie fiction, survivors often stress the importance of weapons that kill quietly. After all, when facing so many challenges in a broken civilization, why make your life tougher by firing a gun and announcing yourself to a mob of undead cannibals? For me, this begs a more probing question: just how many zombies would your gunfire attract? For your post-apocalyptic convenience, I have created a table that gives you a rough idea.
The math is based on the assumptions that 1) Zombies are slow and stagger around at a speed of about one mile per hour; 2) Zombies don't diffuse very much geographically and can be more or less found in their area of origin; and 3) About 75% of the world population has become infected (the other 25% are either survivors or have been killed in a way that prevents reanimation). Granted, these are very big assumptions, but they do allow a starting point in estimating the size of the crowd you will attract by "going loud." For instance, if you have been shooting for fifteen minutes, you will have drawn every zombie within a quarter-mile radius. In rural Wyoming, that's not such a big deal; in Mumbai, India, that's a fatal problem.
Wherever you find yourself, it's key to displace as soon as you can after the shooting has started, because the undead will be converging on your position in numbers that grow geometrically. And it won't be just your immediate position, but the entire area that will be thick with them.