Enter your stored volume, headcount, and daily usage to get days of supply
Stored water supply
Stored Volume
People
person(s)
Daily usage per person
Quick presets:
Daily Usage per Person
⚠ Please enter valid values greater than zero for all fields.
Your Results
Your Supply Lasts
—
Days of Water
Weeks of Supply
— wks
Total Litres
— L
Total US Gallons
— gal
Daily Group Use
— L/day
L per Person per Day
— L
Water Weight
— kg
Stockpile Duration Overview
📖 How To Use
How to Use This Calculator
Find out exactly how long your emergency water stockpile will last in under 60 seconds:
Enter your stored water volume
Count up all your water containers — jerry cans, tanks, bottles, barrels. Enter the total. Switch the unit dropdown to match your measurement (litres, US gallons, UK gallons, or cubic metres).
Enter number of people
Include everyone who will draw from this supply — family members, dependents, and any guests you're planning for.
Set daily usage per person
Use a preset (CDC/FEMA minimum, hot climate, WHO basic, intermediate, or comfortable household) or type in your own figure. Emergency conditions almost always mean lower usage — drinking and cooking only, no showers or laundry.
Hit Calculate
The result shows days of supply, readiness status, weekly breakdown, and total group consumption rate. Copy or print for your emergency plan.
Tip: CDC and FEMA recommend at least 1 US gallon (3.8 L) per person per day for drinking and sanitation, for at least 3 days, and a 2-week supply if possible. Store more for hot climates, pregnancy, illness and pets — in very hot weather, needs can double.
📐 The Formula
Water Stockpile Duration Formula
The calculation is straightforward:
Days of Supply = Total Water (L) ÷ (People × Daily Usage per Person in L)
Weeks = Days ÷ 7
Total Group Daily Consumption = People × Daily Usage per Person
This calculator converts all volume inputs to litres internally. Mixed units are handled automatically — just pick the right unit in each dropdown.
Daily Water Use Benchmarks
Scenario
L/person/day
US gal/person/day
Notes
Drinking only (survival)
2.5–3
0.7–0.8
Water intake alone; more in heat (WHO)
CDC / FEMA minimum
3.8
1.0
Drinking and basic sanitation
Hot climate / pregnancy / illness
7.6+
2.0+
Needs can double in very hot weather
WHO emergency basic needs
7.5–15
2.0–4.0
Drinking, cooking and basic hygiene
WHO intermediate access
~50
~13
Adds bathing and laundry
Typical developed-world household
100–200
26–53
Normal household use
Sources are listed at the bottom of this page.
Days of Supply for a Household of 4
Stored Volume
At 3.8 L/day each
At 15 L/day each
At 50 L/day each
50 L
3.3
0.8
0.25
100 L
6.6
1.7
0.5
200 L
13.2
3.3
1.0
500 L
32.9
8.3
2.5
1,000 L
65.8
16.7
5.0
2,000 L
131.6
33.3
10.0
🔍 Use Cases
When to Use This Calculator
Hurricane & Flood Preparedness
CDC and FEMA suggest a 2-week water supply at home if you can store it, and at least 3 days as a bare minimum. Use this calculator to verify your current stores meet that target — then size up if they fall short before an event hits.
Off-Grid Living
If you're running on rainwater collection or a borehole with uncertain yield, knowing exactly how many days your tank covers gives you a concrete trigger point for when to ration or seek a top-up supply.
Bug-Out & Go-Bag Planning
Water weighs 1 kg per litre. Every litre you carry in a bug-out bag is weight you're hauling on foot. This calculator lets you trade off days of supply against carry weight so you can make a realistic plan, not a wishful one.
Apartment Stockpiling Without a Tank
Many urban dwellers store water in bathtubs, large bottles, or WaterBOB inserts. Knowing the litres in those containers gives a real duration figure — which is almost always much shorter than people assume.
Remote Worksite Supply Planning
Construction crews, mining camps, and research stations often operate where water delivery is intermittent. Use this calculator to plan resupply intervals based on headcount and actual usage rates.
❓ FAQ
Frequently Asked Questions
How do I calculate how long my water stockpile will last?
Divide your total stored volume (in litres) by the total daily consumption of your group (people × litres per person per day). The result is your days of supply. This calculator does that math instantly and converts all common units automatically.
How much water should I stockpile per person for emergencies?
CDC and FEMA recommend at least 1 US gallon (3.8 litres) per person per day, for at least 3 days, and a 2-week supply if possible. For a family of 4, a 2-week supply at that rate is 3.8 × 4 × 14 = about 213 litres (56 gallons). WHO's emergency basic-needs range is 7.5–15 litres per person per day, which also covers cooking and hygiene.
How long can stored water last before it goes bad?
For store-bought bottled water, CDC says to follow the expiration date on the bottle. If you fill your own containers with tap water, CDC advises replacing it every 6 months. Store it in clean, food-grade containers away from light and heat. Use our Chlorine Dosage Calculator for precise treatment amounts.
What is a good water stockpile duration for emergencies?
CDC and FEMA set 3 days as the minimum and recommend a 2-week supply if you can store it. For off-grid living or areas where outages can last longer, many households aim for 30 days or more. Anything under 3 days leaves you exposed in even a short outage.
Does this calculator account for water for pets?
Not automatically. To include pets, convert your pet's daily water consumption to litres and either add it to the per-person daily figure, or treat each large dog as roughly 0.25–0.5 additional people in the headcount field. A common veterinary estimate for dogs and cats of 2–70 kg is 30 mL × body weight in kg + 70 mL a day (MSD Veterinary Manual), so a 15 kg dog needs roughly 0.5 litres, and more in hot weather. Ready.gov lists extra water for pets as part of an emergency kit, and CDC suggests storing more than the 1-gallon minimum when you have pets.
How many litres of water is in a standard 55-gallon drum?
A 55 US gallon drum holds approximately 208 litres. At FEMA's minimum rate of 3.8 L/person/day, a single drum provides one person with roughly 55 days of supply, or a family of 4 with about 13.7 days. You can enter this directly into the calculator using the US gallons option.
Should I plan for more water in hot climates?
Yes — significantly more. In hot climates or during physical exertion, individual water needs rise sharply — Ready.gov notes they can double in very hot temperatures. CDC and FEMA note that pregnant women, sick people and anyone in a hot climate need more than the standard minimum, and in very hot weather needs can double. Use the "Hot Climate" preset (2 gallons per person per day) as a starting point.
How do I calculate water stockpile duration in gallons?
Select "US gal" in the stored volume dropdown and enter your total gallons. Then select "gal/day" in the daily usage dropdown. The calculator converts everything to litres internally and displays the correct days of supply. You don't need to do any manual unit conversion.
✅ Sources & Review
Sources and review
The benchmarks and storage advice on this page come from these references:
WHO/WEDC Technical Notes on Drinking-Water, Sanitation and Hygiene in Emergencies, Note 9: How much water is needed in emergencies — 7.5–15 L per person per day.
WHO, Domestic Water Quantity, Service Level and Health (Howard & Bartram) — service levels including intermediate access (~50 L).
Reviewed by John Mac, PE, Water Systems Specialist
Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.
