When the tap runs dry or the roads close, the first questions are simple: how much water, in what containers, and how much food? This calculator answers them for a household or a workplace sheltering in place. Enter who is in the group, the weight of any pets and the days you want to cover, and it returns gallons and liters of water, the containers that hold them, and the calories your food supply should provide. It is preparedness arithmetic based on public guidance, not medical or veterinary advice.
How the calculator works
Water starts from the federal baseline. Ready.gov and the CDC both say to store at least one gallon per person per day, for drinking and basic sanitation. The CDC asks for at least three days and suggests a two-week supply if you can manage it. Children count as a full person. Pets are counted by weight at one fluid ounce per pound per day, a common rule of thumb for dogs and cats; check with your vet, since diet, size and health change it. Ready.gov notes that water needs can double in very hot temperatures, so the very hot weather option multiplies every line by two, pets included.
Gallons = (adults + children) × 1 × days × heat factor + pet pounds × 1 fl oz ÷ 128 × days × heat factor
The heat factor is 2 in very hot weather and 1 otherwise. Liters are gallons × 3.785.
Containers are always rounded up. The tool counts 7-gallon jugs, 5-gallon jugs, and cases of 24 half-liter bottles (16.9 fl oz each, about 3.17 gallons a case).
Food is counted in calories:
Calories = (adults × calories per adult + children × calories per child) × days
The defaults are 2,000 calories per adult and 1,400 per child each day. Children vary widely: a toddler may need far less than 1,400, a teenager as much as an adult. Set it for your actual children, and raise the adult figure for heavy cleanup work.
Worked example
The tool opens with 2 adults, 1 child, pets weighing 40 pounds in total, 3 days and normal weather, at 2,000 calories per adult and 1,400 per child.
- Adults: 2 gallons a day × 3 days = 6 gallons.
- Child: 1 gallon a day × 3 days = 3 gallons.
- Pets: 40 pounds × 1 fl oz = 40 fl oz a day, about 0.31 gallons. Over 3 days that is about 0.94 gallons.
- Total: 6 + 3 + 0.94 = about 9.9 gallons, or about 37.6 liters.
- Containers: two 7-gallon jugs, or two 5-gallon jugs, or 4 cases of half-liter bottles. Two 5-gallon jugs cover 9.9 gallons with almost nothing to spare; the 7-gallon option leaves slack.
- Food: 2 × 2,000 × 3 = 12,000 calories for the adults, plus 1,400 × 3 = 4,200 for the child, for 16,200 calories in all.
Switch on very hot weather and the water doubles to about 19.9 gallons (about 75.2 liters): three 7-gallon jugs, four 5-gallon jugs or seven cases. Stretch the same family to the CDC's two-week target in normal weather and you need about 46.4 gallons, seven 7-gallon jugs and 75,600 calories of food. That is a closet shelf, not a kitchen cupboard.
Storage, rotation and the people who need more
Commercially bottled water is the simplest choice; observe its expiration date. If you fill your own food-grade containers, Ready.gov and the CDC both say to replace the water every six months. Keep everything cool and dark, away from fuel and chemicals, with the fill date written on each container.
If supplies run short, Ready.gov gives a rolling boil for one full minute, or 1/8 teaspoon of household bleach per gallon, stirred and left for 30 minutes. The CDC's emergency water page also covers filtering and UV light.
The one-gallon baseline is a floor. Ready.gov notes that children, nursing mothers and sick people may need more water, and the CDC adds pregnant women. Anyone on medication should ask a doctor or pharmacist whether it changes their fluid needs. For babies, Ready.gov suggests ready-to-feed formula; if you must mix powdered formula, use bottled or boiled water and add that volume on top of the totals here. Plan medical needs with a professional, not a calculator.
Rotate food the same way. Choose things the group will eat that need no cooking, refrigeration or extra water, such as canned meats and vegetables, peanut butter and protein bars, and pack a manual can opener. Dried foods that need rehydrating add to your water total.
For a workplace, the hurricane season readiness guide sets out when to check supplies as a storm approaches. Heat waves raise water needs and can bring boil-water notices when the grid struggles; see our extreme heat and grid stress playbook.
The rest of the kit beyond water and food
Ready.gov's basic kit list goes well past the pantry: a battery-powered or hand-crank radio, a NOAA Weather Radio with tone alert, a flashlight, a first aid kit, and copies of important documents in a waterproof, portable container. At a reception desk, a weather alert radio with county coding sounds only for alerts covering your area. The picks below cover the rest.
Readiness kit
| Category | Pick | Why it is on the list | Link |
|---|---|---|---|
| Crank radio and light | FosPower hand-crank solar radio | Hand crank, solar and battery power in one: radio, flashlight and a phone top-up when nothing else works. | Shop on Amazon |
| Lighting | Lepro rechargeable LED lantern | Bright area light for a stairwell or meeting room, recharged by USB. | Shop on Amazon |
| First aid kit | Be Smart Get Prepared 326-piece first aid kit | A wall-mountable kit that covers a small office and meets the OSHA and ANSI contents list. | Shop on Amazon |
| Document safe | SentrySafe fire and water resistant file box | Holds the printed plan, insurance papers and recovery keys where a fire or a leak will not reach them. | Shop on Amazon |
How we chose them: each pick comes from the manufacturer's specifications and published reviews; our staff did not test them. If you plan to keep phones, a router or a small fridge running, the power station runtime calculator shows how long a battery will last.
Sources
- Ready.gov, Water.
- Ready.gov, Food and Build a Kit.
- Ready.gov, Pets.
- CDC, How to Create and Store an Emergency Water Supply.
- CDC, How to Make Water Safe in an Emergency.
Frequently asked questions
How much water should I store per person?
At least one gallon per person per day, for drinking and basic sanitation, as Ready.gov and the CDC advise. Plan for at least three days and, if you can, two weeks. Store more for hot climates, nursing mothers, pregnant women and anyone who is ill.
How much water does a dog or cat need in an emergency?
A common rule of thumb is one fluid ounce per pound of body weight per day, so a 40-pound dog needs about 40 fluid ounces, roughly a third of a gallon. Diet, activity, heat and health change that figure, so confirm it with your vet.
How long does stored water last?
Commercially bottled water lasts until its printed expiration date. Replace water you bottle yourself every six months, as Ready.gov and the CDC advise.
How many calories should an emergency food supply provide?
The calculator defaults to 2,000 calories per adult and 1,400 per child per day, so two adults and one child need 16,200 calories for three days. Adjust for age, workload and special diets.
Do I need more water in hot weather?
Yes. Ready.gov says water needs can double in very hot temperatures, so the very hot weather setting doubles every line. For the default family, three days of water goes from about 9.9 to about 19.9 gallons.