Emergency water calculator
This emergency water calculator works out how much drinking water to store. Ready.gov (FEMA) says to store at least one gallon of water per person per day for several days; a family of four needs 12 gallons for three days.
Example: People in the household 4 · Days 3 · Unit: gallons (US) · Water per person per day 1 · Container size 1 → Water to store: 12 gal (45 L) of water – 12 containers of 1.. Source: Ready.gov (FEMA), Water: at least one gallon of water per person per day for several days, for drinking and sanitation; in very hot temperatures water needs can double (read 10.10.2026). Updated: .
How it is calculated
Water to store = people × days × gallons per person per day. Ready.gov, the preparedness site of the U.S. Federal Emergency Management Agency (FEMA), says to store at least one gallon of water per person per day for several days, for drinking and sanitation. It adds that a normally active person needs about three quarters of a gallon of fluid daily, from water and other beverages.
Emergency water at one gallon per person per day
| People | 3 days | 14 days |
|---|---|---|
| 1 | 3 gal | 14 gal |
| 2 | 6 gal | 28 gal |
| 4 | 12 gal | 56 gal |
A family of four storing water for three days needs 12 gallons, about 45.4 liters (1 gallon = 3.785 L, NIST). Ready.gov notes that children, nursing mothers and sick people may need more water, that a medical emergency might require additional water, and that in very hot temperatures water needs can double – so for a hot climate you can enter 2 gallons per person per day.
Storage tips from Ready.gov
- Buy commercially bottled water and store it in the sealed original container in a cool, dark place.
- If you fill your own containers, use food-grade water storage containers; water that has not been commercially bottled should be replaced every six months.
- Never ration drinking water unless ordered to do so by authorities.
To convert between liters and gallons, use the liters to gallons converter; for an emergency bag, the packing list generator helps.
Frequently asked questions
How much water should I store for an emergency?
Ready.gov says at least one gallon per person per day for several days. For one person and three days that is 3 gallons.
How many gallons does a family of four need for two weeks?
56 gallons at one gallon per person per day (4 × 14 × 1 gallon), about 212 liters.
Is one gallon only for drinking?
No. Ready.gov counts the gallon for drinking and sanitation; a normally active person needs about three quarters of a gallon of fluid per day.
Do I need more water in hot weather?
Yes. According to Ready.gov, water needs can double in very hot temperatures.
How often should stored water be replaced?
Ready.gov advises replacing water that has not been commercially bottled every six months.
Sources and legal basis
- Ready.gov (FEMA), Water: at least one gallon of water per person per day for several days, for drinking and sanitation; in very hot temperatures water needs can double (read 10.10.2026)
- NIST SP 811, Appendix B.8: 1 gallon (U.S.) = 3.785 412 L (read 10.10.2026)
As of: · Editorial policy
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