Planning Tool
Emergency Water Storage Calculator
Turn the published allowance into your household’s number: gallons, pounds, and how many containers of the size you actually own.
How much water should your household store?
Uses at least 1 gallon per person per day, the CDC and Ready.gov allowance for drinking and sanitation.
How this is worked out. Gallons is people × days × 1, doubled if you tick very hot weather (Ready.gov: water needs can double in very hot temperatures). Containers is gallons ÷ container size, rounded up. Weight is gallons × 8.329 pounds (USGS, water at 70°F), before the containers themselves. Every number is arithmetic.
What it will not calculate. No extra amount for infants, nursing mothers, illness or pets, because Ready.gov says these needs may be higher without publishing a figure. Add a margin for them. The calculator also never says how long water will stay good; for that, see the storage-life rules below.
Second tool
How many gallons does a container or tank hold?
A container's capacity in gallons is its inside volume in cubic inches divided by 231, the number of cubic inches in one U.S. gallon.
Capacity from inside measurements
Measure the inside, not the outside, in inches. Pick the shape.
How this is worked out. Box: length × width × height ÷ 231. Cylinder: 3.1416 × (diameter ÷ 2)² × height ÷ 231. Weight is gallons × 8.329 pounds. The result is geometry, not the manufacturer's rated capacity; if the maker states a capacity, that figure wins.
Assumptions
The figures this calculator uses
This emergency water storage calculator uses five published figures and nothing else.
| Figure | Value | Source |
|---|---|---|
| Daily allowance | At least 1 gallon per person per day, for drinking and sanitation | CDC; Ready.gov |
| Minimum supply | 3 days | CDC |
| Preferred supply | 2 weeks, if possible | CDC |
| Hot weather | Needs can double | Ready.gov |
| Weight of water | 8.329 pounds per U.S. gallon at 70°F | USGS |
Limits
What to do with the result
The calculator's answer is the least your household should store, and three checks turn it into a workable supply.
Add a margin. Needs can be higher for infants, children, older adults, pregnancy, illness, pets, hot conditions, and physically demanding activity.
Check the weight per container. A 5-gallon jug holds about 42 pounds of water; a 55-gallon barrel about 458 (both calculated). If you cannot lift a container safely, choose a smaller size.
Plan the rotation. The CDC says to replace water you store yourself every 6 months. Sealed commercial bottled water follows its printed date instead.
One barrel, in smaller containers
- 55 galone barrel, about 458 lb of water: fixed in place once full
- 11 × 5 galthe same water in jugs of about 42 lb each: carryable, easier to rotate
Where to go from here: how to store water long term covers placement and labelling, and best emergency water storage containers compares the formats.
Questions
Common questions about calculating water storage
Short answers to the questions people ask alongside the calculator.
Store at least one gallon per person per day for at least three days, and a two-week supply if possible, according to the CDC. A family of four needs 12 gallons for three days and 56 gallons for two weeks, before adding anything for heat, illness, infants or pets.
Measure the inside in inches. For a box shape, multiply length by width by height and divide by 231. For a cylinder, multiply 3.1416 by the radius squared and by the height, then divide by 231. The answer is in U.S. gallons. A manufacturer's stated capacity takes priority over a measured estimate.
Water weighs about 8.329 pounds per U.S. gallon at 70°F, according to the U.S. Geological Survey. A full 5-gallon jug holds about 42 pounds of water and a full 55-gallon barrel about 458 pounds, not counting the container itself.
No. Ready.gov's water guidance does not publish a per-animal figure, so the calculator does not invent one. Add water for pets on top of the household result.
Sources
Where these figures come from
Every figure the calculator uses comes from one of these sources, checked in September 2026.
- Centers for Disease Control and Prevention, “How to Create and Store an Emergency Water Supply” (reviewed June 27, 2025). cdc.gov — 1 gallon per person per day for 3 days; 2-week supply if possible; replace home-filled water every 6 months. Checked September 2026.
- Ready.gov, “Water.” ready.gov — at least 1 gallon per person per day for drinking and sanitation; needs can double in very hot temperatures; higher needs for children, nursing mothers and sick people. Checked September 2026.
- U.S. Geological Survey, “Water Density.” usgs.gov — 8.329 pounds per U.S. gallon at 70°F. Checked September 2026.