I don't keep anything more than a ballpark, in-my-head estimate, and then only on certain guns. If I bought an older, used gun, I don't even bother, for example.
A gunfight is not the time to learn new skills.
If you ever have a real need for more than a couple of magazines, your problem is not a shortage of magazines. It's a shortage of people on your side of the argument. -- Art Eatman