Um, they should be between 3 and 18 inches. Smaller than that and they get lost and you find them several months later with all sorts of inedible things growing on them. Longer than that and they just don't fit on the shelf.

Surely you're not asking or assuming that there is some magic formula for refrigeration that applies to all – or even most – foods. There is not. Some fish does not fare well for even a full day in the refrigerator. A canned ham, even by our government's über-safe estimates, can last at least 9 months. Most foods fit somewhere in between.

The variables are enormous, though. What food are we talking about? How is it packaged? How fresh was it when you bought it? How fresh was it when you got it home? Has it been opened? How cold is your refrigerator? Where is it stored in the refrigerator?

Most products that require refrigeration are stamped by the manufacturer with a sell-by or use-by date. If the variables listed above (freshness, safe temperature, safe storage) have been managed well, your food should last until the use-by date – perhaps a little longer. If you put it in the freezer for a while (which is a great way to store most foods safely) and then thaw it in the refrigerator, use it right away, as the use-by date is most likely no longer relevant and it is unlikely that you remember how close to the use-by date you put it in the freezer.