The Prep NestEmergency Water Storage Calculator
How much water your household needs, in gallons, litres, weight and containers. No email, no sign-up.
| Planning for | Gallons | Litres | Weight |
|---|---|---|---|
| 3 daysThe 72-hour minimum | 12 | 45 | 100 lb |
| 2 weeksWhat the CDC suggests at home | 56 | 212 | 467 lb |
| 1 monthExtended self-sufficiency | 120 | 454 | 1001 lb |
Two weeks, in things you can actually buy
- 18 × Cases of 24 half-litre bottles
- 12 × 5-gallon jerry cans
- 2 × 55-gallon drums
Weight is the full figure, at about 8.34 lb per gallon. A 55-gallon drum cannot be moved once filled, so plan where it goes before you fill it.
Why the weight column matters
One gallon per person per day is the figure everybody quotes, and it is correct. It is also the point at which most advice stops, which leaves you to work out for yourself what that means in containers, in floor space and in pounds.
A two-week supply for a family of four at the minimum rate is 56 gallons. That is about 467 pounds, which is a decision about where in your home it goes rather than about how much it costs. At the higher rate it is 112 gallons and over 900 pounds, which for most households means splitting the store rather than stacking it.
Why there are two rates
Ready.gov and the CDC both set one gallon per person per day, covering drinking and sanitation together. The CDC notes that a normally active person needs about three quarters of a gallon of fluid a day, which leaves roughly a quarter of a gallon for everything else.
South Carolina's Emergency Management Division tells its residents two gallons per person per day, split as one for drinking and one for cooking and washing. Neither is wrong. One gallon is the survival minimum; the second is what makes a fortnight bearable rather than merely survivable. Clear the first before you plan the second.
What to do with the number
Store it in food-grade containers, never in anything that previously held chemicals or in old milk and juice jugs. Water you bottle yourself must be replaced every six months; commercially bottled water keeps to its printed date in the sealed original container. Mark every container with the date you filled it.
Then add a way to make more, because stored water is finite by definition. Our water storage guide covers containers and rotation in detail, and the water filtration page compares what each treatment method does and does not remove.
What this calculator assumes
The gallon rates are the published federal and state figures above. The weight is arithmetic at 8.34 lb per US gallon. The pet figure is a planning convention, not a published standard: each cat or dog counts as a quarter of a person, which is a reasonable allowance for a typical household animal and not a veterinary recommendation. The CDC advises storing more than the baseline for pregnant women, people who are ill, pets and hot climates, and this calculator does not attempt to model any of those; treat its output as a floor.