So how much ammunition do you really need? That depends on what you are preparing for doesn't it? Obviously if you are looking at long term survival, for our purpose here lets say longer than 6 months, compared to a shorter term event of maybe 90 days or so, your ammunition needs vary greatly. One thing I can tell you, you most likely can't get it all in your gun safe.
Consider this, if you are anticipating a short term emergency then what you are really looking at is having ammo to protect yourself and loved ones and maybe hunting and obtaining food. That means that if you have approximately 500 rounds per rifle and 250 rounds per handgun you should be good to go. Bolt action rifles require less so maybe 250 rounds will be fine for them as well. Shotguns can be used in either a food gathering role or as a defensive weapon, having both types of shells on hand is important so you need to adjust your supplies accordingly.
Now for those who are looking at what most consider to be the true survivalist scenario, a TEOTWAWKI event your needs will be much greater. In this type of emergency or event that could last for some time you will need to adjust the amount of ammunition you have on hand. A minimum of 1000 rounds of rifle ammunition per weapon should be your goal. For any handgun 500 rounds per weapon and for shotguns at least 250 rounds of either defensive or hunting shells or both should be kept on hand. Consider this, for long term events hunting will be more prevalent as a food source meaning more ammunition. At some point you may need to practice firing your weapons if for no other reason to ensure they still work properly and to keep your marksmanship skills sharp. Again, more ammunition. Also keep in mind that for some reason some of your supplies may get stolen, damaged or destroyed and the longer the event goes on the greater the odds are of those things happening.
Resupply of all of your stocks will be important before, during and after the event. Understand that it may be sometime before you can just walk into Wal Mart and buy a box or two of ammo and go on your way. Proper storage and security is almost as important as having the ammo to begin with. Keeping your ammunition away from prying hands and eyes and keeping it stored in a cool dry place, the key words there being cool and dry, are needed to ensure you have it when you need it. Think about carrying a handgun everywhere you go everyday, this is what you will be doing in a TEOTWAWKI event, think about using your rifle everyday for home security, this is what you will be doing in a TEOTWAWKI event. Now ask yourself if you have enough ammo to do that comfortably and throw in expending a few rounds every week if for nothing else hunting. That is the scenario you are looking at, no stores with ammo for you to buy and a constant use of your firearms and the slow drain of your supplies.
Granted, where you live will have some bearing on how much and what type of ammunition you need but if you follow my simple guideline for longer term compared to shorter term events you should be fine. Having more is better than having less, just food for thought.