The 72-Hour Kit, By the Numbers

Seventy-two hours is the planning window behind the classic emergency kit: FEMA's guidance is to keep at least a three-day supply that can carry your household without stores, tap water, or electricity. The encouraging part is that a 72-hour kit is not a lifestyle or a shopping spree. It is a short series of small calculations, each of which fits on the back of an envelope, and once you run them the packing list mostly writes itself. Here is the arithmetic, one number at a time.

Start with 3 gallons per person

Water is the anchor. The standing rule from FEMA and Ready.gov is one gallon per person per day, split roughly in half: about two quarts for drinking and food preparation, and two quarts for sanitation, meaning hand washing, teeth, and basic cleanup. Three days therefore means 3 gallons per person, and a family of four is planning around 12 gallons before a single can of food goes in. In retail terms, a standard 24-pack of 16.9 fluid ounce bottles holds about 3.17 gallons, so one case per person is a tidy approximation of the whole three-day target. Two footnotes the rule itself carries: children, nursing mothers, sick people, and hot climates all push the number up, and if supplies ever run low, the official guidance is blunt - never ration drinking water. The water storage calculator runs this exact rule against your household and shows the gap in gallons.

Then 6,000 calories per person

Food is the second calculation, and the planning figure is the same one printed on every nutrition label: 2,000 calories per day. Over three days that is 6,000 calories per person, or 24,000 for that same family of four. The useful discipline is to shop the kit in calories rather than in items, because "a few cans and some granola bars" can land almost anywhere on the scale. Favor food that needs no cooking or almost none, that your household already eats, and that tolerates sitting in a closet. The food storage calculator works in these same units, which makes it easy to extend the three-day kit into the two-week pantry later without redoing any thinking.

Now the hard number: 25 pounds

Here is where the arithmetic turns honest. A gallon of water weighs a little over 8 pounds, so one person's 3-gallon allocation comes to roughly 25 pounds before you pack any food, clothing, or gear. Water is the heaviest thing in any kit by a wide margin, and no amount of clever packing changes that. The practical answer is to split the kit in two: a stay-home supply that never needs lifting, holding the full three days and ideally much more, and a smaller grab-and-go bag that carries about one day of water per person plus a way to make more safely. That second part is what the purification methods guide covers: a purification option weighs ounces and stands in for gallons you cannot carry.

The volume check

Weight is only half the physical reality; the other half is space. A case of bottled water is roughly the size of a large shoebox, and a family of four needs four of them for water alone, plus a tote or two of food and gear. That footprint fits under a bed, at the bottom of a closet, or on one garage shelf, which is exactly the point: the three-day kit is small enough that "no room" is rarely the true obstacle. What actually kills kits is scattering, with water in the garage, food in the pantry, and the flashlight wherever it was used last. The kit only counts if it is one pile in one known place that every adult in the house can find in the dark.

The head start already in your kitchen

One number in your favor: the kit is rarely the first food you eat. The USDA's guidance is that an unopened refrigerator keeps food safe for about 4 hours, and a freezer holds for about 48 hours if full or 24 if half full, doors kept closed. In most outages that means the first day or so runs on what you already own, and the kit's 6,000 calories per person start later than hour zero. The blackout food safety guide covers how to spend that head start without gambling on anything doubtful.

The items the math does not capture

Once water and calories are settled, the rest of the kit is light in both senses. A flashlight and spare batteries, a battery or hand-crank radio, a basic first aid kit, any prescription medications your household cannot skip, copies of key documents, a little cash in small bills, a manual can opener if any of the food needs one, and sanitation basics like soap and garbage bags. None of these need arithmetic, but they do need the same discipline as the food: check that the batteries still work and the medications have not expired when you check everything else.

Round in the right direction

One last rule ties all the numbers together: round needs up and coverage down. If the math says 11.3 gallons, store 12. If your food pile probably covers three days, count it as two until you have added it up in calories. The calculators on this site are built to lean the same conservative way, and the three-day kit deserves the same margin. Whether the situation ends up calling for staying put or leaving, seventy-two hours of margin is what buys you the calm to make that call well instead of making it in a checkout line.