Packing is an art form, and some people are naturals at it. But for those of us who aren't naturally talented at squeezing a week of clothing into a carry-on, data can save us. Numbers blog FlowingData points to calculations and charts from Reed Kennedy and Carrie Smith on how much underwear you're going to need for your next trip.
The idea is simple: use the top line to find the number of days you'll be away from home. On the left side, find the number of pairs of underwear you might hypothetically bring along. The point where those two meet in the chart shows how many times you'll have to do laundry on your trip in order to keep wearing clean underwear.
The numbers in gold represent supreme efficiency — the points at which you will bring back zero clean underwear.
True, underwear is for most of us only a tiny portion of our luggage, but really, the chart can work on any article of clothing you only wear once (socks, t-shirts, etc.).
But there are a few caveats to Kennedy and Smith's math. One is that this chart assumes one pair of underwear per day. For example, if you work out on your trip (and if you wear underwear when you work out), you may need more. The chart also assumes that you'll do laundry only when you're on your last pair (which just feels like cutting it close).
So there may be a reason to pack yourself a cushion. And for that situation, never fear: numbers can still help. Smith and Kennedy also have a second chart that helps you figure out how inefficient your undie-margin-of-error is.