The calculator
Shelter-in-place uses 2 meals and 3 litres of water per person per day. On the move (heat, walking, debris) uses 3 meals and 4 litres. Two snacks count as one light meal. The runway is the minimum of food-days and water-days, floored — a leftover half-day is not a plan.
Group size
Activity
Meals on hand
Ready-to-eat counts. A big pot of stew = how many bowls?
Snacks
Two snacks ≈ one light meal in this estimate.
Water (litres)
What you can actually pour. Not the stream down the hill.
Runway
3DAYS
Food and water run out together — unusual, and useful.
Meal-equivalents
15
People
2
Food days
3
Water days
3
Field estimate, not nutrition science. 2 snacks ≈ 1 light meal. Does not model children, illness, or 40 °C heat.
Water need — worked numbers
Water is usually the limiter. A family of four with 40 litres and a cupboard of cans will hit thirst before hunger if they stay active. Treat the number as a reason to fetch or purify water today, not as permission to wait until day six.
What this will not do
It does not read barcodes, model infants, or promise that 3 L is enough at 40 °C. The app can estimate a pantry from a typed list with on-device AI; this page is the same arithmetic without that model. Purification methods live on the water hub — litres of dirty river do not count until they are drinkable.
Further in the library — titles only
5 titles · 413 articles in this cluster · full text in-app
- 01Water Storage and Purification for Emergencies: CERT-Recommended Methods
- 02Survival Food Priorities: When to Seek Food, Water, or Shelter First
- 03Building a Survival Kit: Level 1, 2, and 3 Essentials
- 04First Aid Kit Checklist for Disaster Preparedness: What Every Home Needs
- 05Hot Climate Survival Kit: Essential Gear for Extreme Heat
Titles only. Full text, regional variants, and tables are in the offline library — they are not published on this site.
Then get it on the phone
You’re reading this with a signal. The situation it describes is one where you won’t have one.