How Many Pairs of Underwear Should I Pack?

Ask this question and you'll get confidently different answers. Trip days plus one. Trip days plus three. Twice the number of days. For a five-day trip that's a range from six pairs to ten, which is not a rounding error. The reason they disagree points at the variable that actually decides it.

Quick Answer

Why the Rules Disagree

The most widely circulated rule comes from British travel expert Amanda Parker, quoted in the Daily Mail and picked up by Travel+Leisure: pack three more pairs than the number of days. Five days, eight pairs. She frames the extra three as a safety net for unexpected swims, last-minute hikes, sweaty travel days, or just wanting something fresh before dinner.

Other published rules land elsewhere. Luxury Travel Magazine suggests no more than days plus one for an ordinary trip, with additions for humid climates where you'll shower twice a day. Tommy John recommends twice the number of days, so fourteen pairs for a week. One travel blogger offers a formula, days multiplied by 1.25 plus days multiplied by 0.5, which yields nine for five days. And the 7-7-7 approach says seven pairs covers three weeks with a weekly wash.

Run those on an identical five-day trip and you get six, eight, nine, and ten. They aren't measuring the same thing. Each one silently assumes a different amount of laundry, a different activity level, and a different tolerance for washing in a sink. Worth noting on the highest number: the source recommending two pairs per day sells underwear.

The Variable They're All Circling

The most rigorous treatment of this comes from a lingerie designer writing about packing strategy, and the method is simple. Don't pack for the trip. Look at your itinerary, identify the days you could realistically do laundry, and find the longest stretch between them. Pack for that stretch, plus a small buffer. If your three-week trip has three laundry opportunities and the longest gap is four days, you're packing for four days, not twenty-one.

That reframe explains why every per-day formula collapses on long trips. The blogger with the 1.25 formula runs it on twelve days, gets twenty-one pairs, notes that that's absurd, and switches to a laundry-cycle formula instead. The 7-7-7 rule is a laundry-cycle rule wearing a trip-length costume.

Real traveler behavior confirms it. On a long-running Rick Steves forum thread, experienced travelers converge on five to seven pairs almost regardless of trip length, including someone who did five weeks on seven pairs and someone who sink-washes every two to four days on five. One traveler tried five pairs for a five-week trip and ended up buying a three-pack, which is a useful data point about where the floor actually is.

Common Mistakes

People pack per-day for long trips, which is how you end up with a bag full of underwear and no room for anything else. A Travel+Leisure writer admitted using an entire packing cube on thirteen pairs for a three-day trip and wearing roughly a third of them.

People assume underwear is small enough that overpacking is free, but in practice thirteen pairs is a packing cube, and that cube is competing with shoes and layers that genuinely can't be washed in a sink overnight.

People plan on doing laundry and then don't. This is the honest failure mode behind the higher recommendations, and the reason a buffer of two or three pairs beyond your laundry-cycle number is worth carrying: it lets a skipped wash slide by a day without becoming a problem.

The Numbers, Practically

For a weekend or a three-day trip, four or five pairs. The formulas barely matter at this length and the buffer costs nothing.

For a week with no laundry, seven to nine. This is the case where days-plus-two lands right, and where days-plus-three is defensible if you're expecting heat or activity.

For a week with one wash midway, five or six. You're really packing for a four-day stretch twice.

For anything longer, stop counting days. Find your longest laundry gap, pack for that plus two or three, and you'll almost always land between five and eight pairs whether the trip is two weeks or two months.

Fabric changes the math too, since quick-drying synthetics and merino can be washed in a sink at night and worn the next morning, which shortens the effective gap. Our comparison of underwear and sock materials for long trips covers which fabrics actually support that and where each one falls down.