How the figures are worked out
Water
The UK government's Be Ready checklist says bottled water for 3 days: 3 litres per person per day for drinking, with more needed for other tasks such as cooking and washing. That is the figure used here for everyone, including children. Cooking dried rice and pasta, washing and flushing all need more, so the calculator can add an extra allowance (our own planning estimate, not an official figure). Pets are worked out at 60 ml per kg of body weight per day, the top of the 50 to 60 ml/kg range given by the Purina Institute (a pet food maker's research body, not a government source).
Food
Food is worked out in calories. An adult is planned at 2,000 kcal a day by default (the NHS says an average man needs around 2,500 kcal a day and an average woman around 2,000 kcal). You can lower it to a rationed 1,600 kcal or raise it for active adults. Children get a share of the adult figure by age: under 1: 30%, 1 to 3: 45%, 4 to 6: 60%, 7 to 10: 75%, 11 to 14: 90%. Babies who are breastfed or on formula need their own milk supply: plan formula separately.
The calories are then split across a mix of long-life foods so the diet is not just carbohydrate: about 45% from rice, pasta, oats and flour, 10% from pulses, 10% from tinned fish, meat or beans, 15% from oil and nut butter, 5% each from tinned fruit and veg, milk powder or UHT milk, sugar and jam, and snacks. It is a starting point, not a diet plan. Swap in what your household will actually eat.
Short cuts vs long stores
- 3 to 7 days: favour food you can eat cold from the tin or packet. A power cut may also take out your cooker.
- 2 weeks and longer: dry staples are cheaper and lighter per calorie, but need water and fuel to cook. Check your power and cooking gas plans.
- Store what you normally eat and use the oldest first, so nothing goes out of date. See rotating your stock.
Storing water
Use clean food-grade containers with a lid. Bottled water keeps until its best-before date unopened; tap water stored in clean containers should be changed regularly. Read our emergency water guide for how to store and treat it.