A community of 100 people needs about 280,000 kcal a day, which is 102.2 million kcal a year, if it plans on a community-wide average of 2,800 kcal per person per day. That average mixes children, adolescents, working adults, the elderly and nursing women at post-collapse activity levels, so it is not a figure for any single adult and must never be applied to one.
Part of Caloric Budget for a Community
Caloric requirements by population are the energy needs of a community summed across its members, which vary by age, sex, activity and season, and which fix how much food must be grown and stored.
One Number For A Community, Not For A Person
A food label’s 2,000 kcal is a reference figure for a sedentary adult. In a post-collapse community almost nobody is sedentary, children need less than adults, labourers need much more, and the mix changes the total. The parent guide therefore plans with 2,800 kcal per person per day as a community average across its sample population of 100. Everything downstream, acres, storage, winter gap, uses that one number, so its meaning must be kept straight: it is a population average over a specific mix, not the need of an adult of any particular size or work.
100 People At 2,800 kcal Need 102.2 Million kcal A Year
- Per day: 100 people × 2,800 kcal = 280,000 kcal.
- Per year: 280,000 × 365 = 102,200,000 kcal, or 102.2 million.
- The same arithmetic for other community sizes, at the same average: 30 people need 30 × 2,800 × 365 = 30.66 million kcal a year; 150 people need 153.3 million.
The parent’s mix for 100 people is shown below. Its ranges describe adults of unstated size, so they are the parent’s working figures, not measurements.
| Group | People | Need (kcal/day) |
|---|---|---|
| Children under 10 | 15-20 | 1,200-1,800 |
| Adolescents 10-17 | 10-15 | 2,200-3,200 |
| Working adults 18-60 | 50-60 | 2,600-4,000 |
| Elderly or disabled | 10-15 | 1,800-2,200 |
| Pregnant or nursing women | 3-8 at a time | add 300-500 above baseline |
Where these ranges come from, and whether they hold together, is in Adult Caloric Needs by Activity Level and Children, Pregnant, and Elderly Adjustments.
Method: Set Your Own Planning Figure
Step 1: Count the community by the groups above, using real ages and jobs, not the sample.
Step 2: Give each group a planning figure from the two linked pages, naming the activity level, body size and sex it assumes.
Step 3: Multiply and add, then divide by headcount to get your own average.
Step 4: Compare with 2,800. If yours is lower, the parent’s figure is conservative for you; if higher, plan for more land and storage.
Step 5: Re-check every season, because the heavy-labour weeks of planting and harvest move the average (Seasonal Labor Calorie Spikes).
Common Mistakes
- Using 2,800 as a per-adult figure. It is below a heavy labourer’s need and above a young child’s.
- Quoting the yearly total without the headcount. 102.2 million kcal is for 100 people only.
- Forgetting that calories are not nutrition. A budget that meets the number with one food can still cause deficiency disease (Nutrition Programs).
Safety
Under-feeding people who do heavy work
A community that plans on the average while its labourers work at the top of the range will slowly lose weight and strength, and children and pregnant women lose first. Watch body weight and energy, and add to the heavy workers’ allocation before they decline (Malnutrition Signs).
What’s Next
- Learn next: Adult Caloric Needs by Activity Level — the adult figures in detail
- Combine with: Crop Calorie Yields Per Acre — converting calories into land