Part of Food Storage Infrastructure
Capacity calculation determines how much food storage space a community needs, how much of each food type to store, and what physical dimensions storage facilities must achieve. Building a cellar too small wastes the harvest; building one too large wastes construction labor and materials. Getting this right requires caloric math, knowledge of food densities, and planning for realistic loss rates.
The core principle: storage must sustain the population from one harvest to the next — a minimum of 12 months — plus a safety reserve of at least 25% to buffer against a poor harvest year. Communities that calculate exactly to their minimum need one bad year to face starvation.
Step 1: Daily Caloric Requirements
Baseline consumption per person per day:
| Activity Level | Daily Calories |
|---|---|
| Sedentary (minimal physical work) | 1,800-2,000 kcal |
| Moderate work (farming, craft) | 2,200-2,500 kcal |
| Heavy labor (logging, construction) | 2,800-3,500 kcal |
| Nursing mother | Add 400-500 kcal |
| Child (5-12 years) | 1,400-1,800 kcal |
| Adolescent | 2,000-2,800 kcal |
A community engaged in rebuilding activities will average 2,500-2,800 kcal/person/day across all ages. Use 2,500 kcal/person/day as a planning baseline for mixed-age communities.
Annual caloric need:
- Population x 2,500 kcal/day x 365 days = total annual calories
- Example: 50 people x 2,500 x 365 = 45,625,000 kcal per year
Reserve factor: Multiply by 1.25 for a 25% safety reserve. In the example: 45,625,000 x 1.25 = 57,031,250 kcal storage target.
Step 2: Caloric Density and Storage Volume
Different foods provide different calories per unit of storage volume. This determines how much physical space is required:
| Food | Calories per kg | Bulk Density (kg/m3) | Calories per m3 |
|---|---|---|---|
| Wheat grain | 3,400 | 750-800 | 2,550,000-2,720,000 |
| Corn (maize, whole) | 3,500 | 720-770 | 2,520,000-2,695,000 |
| Rice (husked) | 3,600 | 750-800 | 2,700,000-2,880,000 |
| Dried beans | 3,400 | 800-850 | 2,720,000-2,890,000 |
| Dried lentils | 3,500 | 750-800 | 2,625,000-2,800,000 |
| Dried peas | 3,300 | 750-800 | 2,475,000-2,640,000 |
| Oats (whole) | 3,900 | 450-500 | 1,755,000-1,950,000 |
| Sunflower seeds | 5,800 | 600-650 | 3,480,000-3,770,000 |
| Dried potato slices | 3,400 | 300-400 | 1,020,000-1,360,000 |
| Salt (for preservation) | 0 | 1,200 | — |
Working example continued:
A community planning to meet 60% of calories from grain (wheat) and 15% from dried legumes (beans), with the remainder from fresh food:
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Grain calories needed: 57,031,250 x 0.60 = 34,218,750 kcal
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Wheat required: 34,218,750 / 3,400 = approximately 10,065 kg
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Storage volume for wheat: 10,065 / 775 (avg bulk density) = approximately 13 cubic meters
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Bean calories needed: 57,031,250 x 0.15 = 8,554,688 kcal
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Beans required: 8,554,688 / 3,400 = approximately 2,516 kg
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Storage volume for beans: 2,516 / 825 (avg bulk density) = approximately 3 cubic meters
Total grain+legume storage volume needed: approximately 16 cubic meters, plus additional space for root vegetables, preserved meats, and handling room.
Step 3: Storage Building Dimensions
Convert volume requirements to building dimensions:
Usable volume vs. building volume: Not all of a storage building can be filled with food:
- Structural elements (walls, floor, roof) reduce usable interior volume by 15-20%
- Aisles and working space for access: at minimum 0.6-0.9 m wide paths between storage
- Headroom for working: minimum 1.8-2.0 m ceiling height
- Bins/shelves do not always pack perfectly: expect 70-80% efficiency in converting floor area to stored volume
A building with interior dimensions of 4 x 5 m (20 m2 floor area) x 2.4 m ceiling height = 48 m3 total volume. After accounting for working space (30% reduction), available storage volume is approximately 34 m3.
Example storage building for 50 people:
- Required volume (grain + legumes): 16 m3
- Additional root vegetables (potatoes, root crops): 8-10 m3
- Preserved meats, ferments, other: 3-5 m3
- Total: approximately 27-31 m3 with 20% efficiency buffer = approximately 35 m3 needed
A single building 4 x 5 m x 2.4 m ceiling provides adequate capacity, with some working room.
Step 4: Root Cellar Sizing for Produce
Root vegetables require different calculations because they are not packed as densely as grain and require humidity control:
Common root vegetable densities in typical cellar storage:
| Vegetable | Bulk Density (kg/m3) | Recommended Storage Duration |
|---|---|---|
| Potatoes | 600-650 | 4-6 months |
| Carrots (in sand) | 700-750 | 5-6 months |
| Beets | 700-750 | 4-5 months |
| Turnips/Parsnips | 650-700 | 4-5 months |
| Cabbage | 400-500 | 3-4 months |
| Winter squash | 300-400 | 4-6 months |
| Onions (in crates) | 450-500 | 4-6 months |
Planning per person per day:
- Vegetables: 300-500 g fresh weight per person per day
- For 50 people over 5 months of storage (150 days): 50 x 400g x 150 = 3,000 kg total
- Volume required: 3,000 / 650 (average bulk density) = approximately 4.6 m3
Add 20-30% for wastage and selection losses during storage: approximately 6 m3 needed for root vegetables.
Step 5: Preserved Food Equivalents
For preserved items (canned, pickled, smoked), calculate by weight and expected consumption:
Preserved meat:
- Target: 30-50 g protein per person per day from preserved meat
- Protein content: smoked pork approximately 25% protein by weight
- Daily requirement per person: 50g protein / 0.25 = 200 g smoked pork per day
- Annual requirement per person: 200 g x 365 = 73 kg per person
- For 50 people: 3,650 kg smoked/preserved meat
- Storage volume (hanging, with spacing): approximately 8-10 m3
Preserved produce (pickles, ferments):
- Allow 0.5-1 liter per person per week
- For 50 people over 52 weeks: 50 x 0.75L x 52 = 1,950 liters
- At 1 L per crock, approximately 2,000 crock units (stackable ceramic crocks)
- Volume: approximately 5 m3
Putting It Together: 50-Person Community
| Storage Category | Quantity | Volume Required |
|---|---|---|
| Grain (wheat, corn, rice) | 10,000 kg | 13 m3 |
| Dried legumes | 2,500 kg | 3 m3 |
| Root vegetables | 3,000+ kg | 6 m3 |
| Preserved meat | 3,600 kg | 10 m3 |
| Preserved produce | 2,000 L | 5 m3 |
| Salt | 500 kg | 0.4 m3 |
| Working space and aisles | — | 12 m3 |
| Total building volume needed | 49 m3 |
A 5 x 5 x 2.4 m building (60 m3) with an additional 4 x 5 m root cellar (40 m3) comfortably meets these needs with room for growth.
Adjusting for Actual Yields
Calculate storage requirements before each harvest season based on:
- Expected harvest yield (be conservative — 70-80% of best-case estimate)
- Population size and age distribution
- Expected supplement from hunting, gathering, and trading
- Actual storage life of available containers
Recalculate annually. A community that grows significantly or shrinks, or that shifts its diet composition, must revise its storage capacity accordingly. Do not assume last year’s calculations remain valid.