Emergency Food Supply Calculator

Three litres of water a day is the figure people under-store most, and it runs out first.

Calories112,0002,000 per serving, in kcal, mL or g

Recipe for4 servingsEmergency food, per day, over 14 days

Water168,0003,000 per serving, in kcal, mL or g

Dry staples28,000500 per serving, in kcal, mL or g

Two thousand calories and three litres of water a day is the usual emergency planning figure. Water is the one that runs out first and the one people under-store most — three litres covers drinking and basic cooking, not washing.

The formula

quantity = per-serving amount * servings

Most recipes scale linearly, and a few do not

Flour, liquid and fat scale straight up with the serving count. What does not is anything governed by surface area or by time: seasoning needs less than proportionally in a large batch, leavening rather more, and cooking times barely move at all because a doubled pan is wider rather than deeper.

Eggs are the awkward one

They come in indivisible units of about 50 g, so a recipe scaled to two and a half eggs has to round, and rounding an egg is a 20 % change in the binding. Beating an egg and weighing out part of it is the honest fix; rounding up and taking a little liquid out is the practical one.

Scaling down is harder than scaling up

Halving a cake recipe leaves quantities that are hard to weigh and a batter too shallow for the tin, and the crust-to-crumb ratio changes. Small batches of anything baked are simply less forgiving, which is why professional recipes are written large and domestic ones rarely go below four servings.

Recipes are starting points

Ovens run hot or cold by 20 degrees, flour absorbs water differently by season and brand, and the same joint of meat cooks at a different rate depending on its shape rather than its weight. Everything here is a planning figure that gets you close enough to start, and the thermometer, the scales and your own notes from last time are what finish the job.