Disaster Stockpile Calculator
Enter your household size and number of days to calculate the drinking water, food, and portable-toilet supplies you need. Based on figures published by the Tokyo Metropolitan Government. Nothing you enter is sent anywhere.
The household size and days you enter are calculated entirely in your browser and never sent anywhere.
Enter household size and days, then press "Calculate".
- Drinking water
- L
- Meals
- meals
- Portable toilet uses
- uses
How to use
- Enter your household size (1 to 20 people).
- Choose the number of days to stockpile for. Use the "3 days" / "7 days" buttons or enter a custom number.
- Press "Calculate" to see the drinking water, food, and portable-toilet quantities you need.
How it works
The figures behind this calculator
This calculator multiplies your household size and number of days by baseline figures widely published by the Tokyo Metropolitan Government (Tokyo Bichiku Navi, the Tokyo Toilet Disaster Prevention Master Plan) and other Japanese disaster-preparedness guidance:
- Drinking water: 3 liters per person, per day
- Meals: 3 meals per person, per day
- Portable toilet uses: 5 uses per person, per day
Every calculation is a simple multiplication of baseline value x people x days, so no rounding occurs except for the bottle-count reference figure, which is rounded up to whole 2L bottles.
How many days should you stockpile for?
Japanese disaster-preparedness guidance commonly recommends "at least 3 days, ideally 1 week." This range accounts for the time it can take for utilities to be restored or relief supplies to arrive, and varies by region and disaster severity. If unsure, start with 3 days and aim for 7 days when storage space allows.
Why household ("gray") water is not included
Water used for flushing toilets, laundry, or washing (as opposed to drinking) is also needed during a disaster, but published guidance on the required amount varies widely (roughly 10 to 20 liters per person per day in some sources), without a single clearly defined figure. To keep this calculator's numbers reliable, it only covers the three items with clear published baselines: drinking water, food, and portable-toilet supplies. Consider filling a bathtub or other containers separately for household water.
What is out of scope
Infant formula, allergy-specific food, pet supplies, and medication are not calculated here, since the right amount depends heavily on each household's circumstances. Use the three figures above as a baseline and add to them based on your own situation.
FAQ
Is the household size or number of days I enter sent anywhere?
No. All calculation happens entirely in your browser, and no network request is made after the page loads.
Why is drinking water calculated at 3 liters per person per day?
This is a baseline figure widely used in Japanese public disaster-preparedness guidance, including materials from the Tokyo Metropolitan Government. It represents the minimum amount needed to stay healthy during a disaster.
Does this include household (gray) water, like water for flushing toilets or laundry?
No. Published guidance on the amount of household water needed varies too widely to give a reliable figure, so this calculator only covers drinking water, food, and portable-toilet supplies, which have clear published baselines.
How many days should I stockpile for?
Common guidance is "at least 3 days, ideally 1 week." Start by checking the 3-day figure for a minimum safety margin, then switch to 7 days if you have the storage space.
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