How this instrument works
Emergency preparedness planning boils down to two numbers: how much water keeps a household hydrated and reasonably clean, and how much food energy keeps everyone fed, for however many days supply lines might be disrupted. FEMA's Ready.gov program has published a simple, durable rule for the water half of that question for years: store one gallon of water per person per day, covering both drinking and basic sanitation needs.
This calculator applies that 1 gal/person/day water rule directly, then pairs it with a general dietary reference of about 2,000 kilocalories per person per day to size the food side of the supply. That food number is a broad average, not a personalized nutrition target — it's meant to help you gauge roughly how much shelf-stable food (in calorie terms) to have on hand, not to replace a proper meal plan.
A commonly cited emergency-preparedness benchmark is 3 days as a starting minimum, with many agencies recommending households build toward 2 weeks when possible, especially in areas prone to longer disruptions like winter storms or extended power outages. This calculator lets you dial in any number of days so you can plan for either scenario, or anything in between.
- Enter your household size — everyone who would be relying on this stored supply, including pets if you're planning separately for them.
- Enter the number of days you want the supply to cover (3 days is a commonly cited starting minimum; 2 weeks is a commonly recommended target).
- Read Water to store for the total gallons to set aside for drinking and basic sanitation.
- Read Approx. food energy needed for a rough kilocalorie total to help gauge how much shelf-stable food to stock.
- Re-run the numbers whenever your household size changes, or before hurricane, wildfire, or winter-storm season if you're in an area prone to one of those.
Worked example — a 4-person household stocking a 2-week supply
A family of 4 wants to build up to the commonly recommended 2-week (14-day) supply rather than stopping at a 3-day starting minimum. Water: waterGal = 4 × 14 × 1 = 56 gallons — that's roughly fourteen 4-gallon jugs, or a mix of stored water and a plan to treat additional water if needed.
Food energy: foodKcal = 4 × 14 × 2,000 = 112,000 kcal total across the household and the full two weeks. Translated into shelf-stable staples, that's the rough calorie budget for canned goods, dried food, peanut butter, and similar non-perishables that don't require refrigeration or much water to prepare.
Compare that to a smaller household on a 3-day starting minimum instead — say 2 people for 3 days needs only 2×3×1=6 gallons of water and 2×3×2,000=12,000 kcal, showing how quickly the totals scale with both household size and the number of days you're planning for.
Questions
Why one gallon of water per person per day?
That figure is FEMA/Ready.gov's long-standing emergency-preparedness guideline, and it covers more than just drinking — a normally active person needs roughly three-quarters of a gallon in beverages alone, with the rest allocated to basic sanitation like hand-washing and food prep. Hotter climates, pregnant or nursing individuals, and anyone who's ill may need more, so treat 1 gallon/person/day as a floor, not a ceiling.
Is 2,000 kcal/day accurate for everyone in my household?
No — it's a general dietary reference figure, not a personalized number. Actual calorie needs vary a lot by age, sex, size, and activity level (children and smaller or less active adults typically need less, larger or more active adults more). Use the calculator's total as a rough planning ballpark for how much shelf-stable food energy to stock, then weight it toward your household's actual composition.
Should I plan for 3 days or 2 weeks?
A commonly cited emergency-preparedness benchmark is 3 days of supplies as a starting minimum, which covers most short-term disruptions like a power outage or a storm that closes roads briefly. Many agencies also encourage building toward 2 weeks where practical, since longer-duration events — extended power outages, severe winter storms, or supply-chain disruptions — can stretch well past 3 days. This calculator works for either target; just change the days input.
Does this water total include water for pets?
Not unless you count them in the household size input. Pets have their own water needs, and the American Red Cross and Ready.gov both recommend planning separately for them — a rough starting point many sources cite is about the same 1 gallon/day/pet for larger dogs, less for small pets, though needs vary by species and size.
What kinds of food should I actually buy to hit this calorie total?
Focus on shelf-stable, non-perishable items that need little or no refrigeration and minimal water or cooking to prepare: canned meats, beans and vegetables, peanut butter, dried fruit and nuts, crackers, granola bars, and ready-to-eat meals. Rotate stock periodically so nothing expires unnoticed, and keep a manual can opener with your supplies — an easy thing to forget until you need it.