Household water and food calculator (U.S. and Japanese guidance)
Enter your household size and the number of days. The calculator shows how much water to store under U.S. and Japanese guidance, and how many meals that many days means. Everything is calculated in your browser; nothing is sent anywhere.
Worked examples
Common household sizes, calculated with the same assumptions.
| People | Days | Water, U.S. guidance | Water, Japanese guidance | Meals |
|---|---|---|---|---|
| 1 | 3 | 3 gal (about 11 L) | 9 L (about 2.4 gal) | 9 |
| 1 | 7 | 7 gal (about 26 L) | 21 L (about 5.5 gal) | 21 |
| 2 | 3 | 6 gal (about 23 L) | 18 L (about 4.8 gal) | 18 |
| 2 | 7 | 14 gal (about 53 L) | 42 L (about 11.1 gal) | 42 |
| 3 | 3 | 9 gal (about 34 L) | 27 L (about 7.1 gal) | 27 |
| 3 | 7 | 21 gal (about 79 L) | 63 L (about 16.6 gal) | 63 |
| 4 | 3 | 12 gal (about 45 L) | 36 L (about 9.5 gal) | 36 |
| 4 | 7 | 28 gal (about 106 L) | 84 L (about 22.2 gal) | 84 |
Assumptions
- U.S. guidance (Ready.gov): "Store at least one gallon of water per person per day for several days, for drinking and sanitation."
- Japanese guidance (MAFF): about 3 liters per person per day, for a minimum of 3 days and preferably a week. These 3 liters are for drinking and cooking; MAFF notes that water for washing food and dishes is needed on top of that.
- So the two figures cover different things: the U.S. figure includes sanitation, the Japanese one includes cooking.
- 1 U.S. gallon is taken as 3.785 liters. Meals are counted as 3 per person per day.
Reading the result
- These are starting points. Ready.gov notes that children, nursing mothers, and sick people may need more water, and that in very hot temperatures water needs can double.
- Pets are not included.
Everyday
Buy a little more water and food than you need, use it as usual, and replace what you use. Japan's agriculture ministry recommends exactly this, and it means your supply is never forgotten in a closet.
When it counts
If the water stops or stores run out for a while, you can get by on what is already at home.
Sources and when we checked them
- Ready.gov (FEMA), "Water" (checked 2026-10-31)
- Ministry of Agriculture, Forestry and Fisheries of Japan, Q&A on emergency drinking water (in Japanese) (checked 2026-10-31)
- Ministry of Agriculture, Forestry and Fisheries of Japan, "How do you store water?" (in Japanese) (checked 2026-10-31)
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