The cropland one person needs is their yearly calories divided by calories per acre, multiplied by a diet factor: at 2,800 kcal a day and the caloric guide’s 2.5 million kcal per acre, a plant-only diet needs 0.41 acre of crops, and every share of calories taken from grain-fed animals multiplies that by the inverse of the animals’ efficiency. With 20% of calories from animals at 15% efficiency the figure is 0.87 acre, and resting land raises it again.
Part of Caloric Budget for a Community
Acres per person by diet type is the cropland needed to feed one person under a given mix of plant and animal foods, derived from calorie need, crop yield and animal conversion efficiency.
Animal Calories Multiply The Land By The Inverse Of Efficiency
Let C be the calories per person per day (2,800 here, the community average), Y the calories per acre (2.5 million, the guide’s diversified average), x the share of calories eaten as animal food, and e the animals’ efficiency (energy out over energy in, fed entirely on cropland grain).
Acres per person = (C × 365 ÷ Y) × [(1 − x) + x ÷ e]
The first bracket is the plant-only base; the second is the diet factor: the plant share is eaten directly, while each animal calorie costs 1 ÷ e plant calories.
Worked Example: The Base And The Table
- Base: 2,800 × 365 = 1,022,000 kcal a year; ÷ 2.5 million = 0.409 acre per person.
- Diet factor and acres, with fallow added by dividing by the productive share (0.75 if a quarter rests, 0.667 if a third rests, the range given in the guide’s fallow rule):
| Animal share x | Efficiency e | Diet factor | Crop acres | With 25% fallow | With 33% fallow |
|---|---|---|---|---|---|
| 0 | none | 1.00 | 0.41 | 0.55 | 0.61 |
| 10% | 15% | 1.57 | 0.64 | 0.85 | 0.96 |
| 20% | 25% | 1.60 | 0.65 | 0.87 | 0.98 |
| 20% | 15% | 2.13 | 0.87 | 1.16 | 1.31 |
| 20% | 10% | 2.80 | 1.15 | 1.53 | 1.72 |
| 30% | 15% | 2.70 | 1.10 | 1.47 | 1.66 |
| 30% | 10% | 3.70 | 1.51 | 2.02 | 2.27 |
- Check one row: x = 20%, e = 15%: (1 − 0.2) + 0.2 ÷ 0.15 = 0.8 + 1.333 = 2.133; 0.409 × 2.133 = 0.872 acre; ÷ 0.75 = 1.163; ÷ 0.667 = 1.308.
- The guide’s total of 1 to 1.5 acres of agricultural land per person fits the middle rows. Its sample plan of 91-128 acres for 100 people is 0.91-1.28 per person.
What The Table Assumes
- Animals eat cropland grain. Animals on pasture that could not grow crops, or on crop residues and kitchen scraps, do not take cropland, so for them the table overstates the cost. The guide’s own rule is to keep animal grain to 10-15% of cropland (Pasture vs Grain-Fed Calculations).
- The efficiencies are the guide’s stated ones; some of them are too high on grain (Feed-to-Meat Ratios by Animal), which would push the acres up.
- A single yield of 2.5 million kcal per acre is applied to the whole plant share.
- The 2,800 kcal figure is a community average, not one person’s need.
- Failure margin, seed saving and pasture are in addition to the table.
Method: Estimate Your Own Acres
Step 1: Set your community’s per-person calories and your real average kcal per acre. Step 2: Decide the share of calories you will take from animals and which animals. Step 3: Choose efficiencies from your own records, not the table. Step 4: Compute acres with the formula, then add fallow and the buffer.
Common Mistakes
- Treating a diet as a moral choice. It is a land budget: the same people eat less on the same land.
- Ignoring pasture. Land that can only be grazed changes the answer.
- Using the average yield for a poor field.
What’s Next
- Learn next: Fallow Rotation and Soil Recovery — the resting land in the last two columns
- Combine with: Land Allocation Planning — the full plan