Knowing how much underwear to pack for a trip can be fraught with problems: how many pairs do you need for a long trip, and what happens if there's... an accident? Don't fear, though, because this chart will help you know exactly what to pack.
Forming part of a wonderful post called Pack Like a Nerd, this chart plots the number of washes you'll need to perform during a trip, given the number of pairs you take with you. Gold numbers refer to the a perfect remainder of zero pairs of clean underwear by the time you get home.
It makes some assumptions: that you'll be wearing underwear when you do a wash, and that you only do laundry when you're wearing your last pair of underwear. But worst of all, it doesn't factor in the inside-out trick. Still, some simple multiplication should help you there. [Pack Like a Nerd via Flowing Data]