How the calculator works
Ready.gov and the CDC both use the same starting point: store at least one gallon of water per person per day for drinking and basic sanitation. The calculator multiplies that by the number of people and the number of days, then adds a separate line for pets.
Total gallons = (people × 1 gallon × days) + (pets × gallons per pet per day × days)
If you tick hot climate, the per-person amount doubles to 2 gallons a day, because Ready.gov notes that in very hot temperatures water needs can double. Ready.gov also says children, nursing mothers and people who are sick may need more, so round up if that applies to your household.
Containers, weight and rotation
- 1-gallon jugs and 5-gallon containers are rounded up, so you never come up short.
- The 55-gallon drum plan shows how many full drums you would need, plus 5-gallon containers for the rest. Drums are heavy and stay where you fill them.
- Weight uses about 8.34 pounds per US gallon, which is why most stored water belongs at home or in the car, not in backpacks.
- Replace by is six months after the fill date you enter. The CDC recommends replacing water you store yourself about every six months; for store-bought water, follow the date on the package.
What it doesn't do
This is a single snapshot for one household. It doesn't track individual containers, what's already stored, or your other kit supplies. Pet amounts vary widely by species, size and activity, so the pet figure is only as good as the number you get from your veterinarian.
Frequently asked questions
Does the one-gallon rule include cooking?
Ready.gov's one gallon per person per day covers drinking and basic sanitation. If you plan to cook with water, rehydrate food or wash more, store extra.
Should I store 3 days or 2 weeks?
Ready.gov describes several days of supplies for a kit, and the CDC suggests at least 3 days and a 2-week supply at home if possible. A common plan is 3 days in a go-bag or car and 2 weeks at home.
Can I fill my own containers?
Yes. The CDC recommends food-grade water storage containers, cleaned and sanitized before filling, and replacing home-filled water about every six months.
Read the full guide
Sources
Results are estimates for planning, not professional advice. Check the official sources above for rules that apply to you.