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How Much Land Feeds One Person

The honest arithmetic behind a number everyone gets wrong

Start with calories, not beds

An adult who is not doing heavy physical work needs roughly 2000 to 2500 calories a day, so about 800000 calories a year. That single number is the whole problem in front of you, and every square metre of ground has to be measured against it.

The arithmetic is simple. Take the yield of a crop in kilograms per square metre, multiply by the calories in a kilogram, and you get calories per square metre. Potatoes at 3.5 kg and 770 calories per kilogram give about 2700 calories from one square metre. Lettuce at 2.5 kg and 150 calories gives 375. That is a seven times difference from the same patch of soil.

Why the quoted figure is usually wrong

You will read that 100 square metres feeds a person, and also that you need 4000. Both are quoted honestly and both are nearly useless, because they answer different questions.

The small figures come from intensive beds growing only the highest calorie crops, in a good climate, worked by someone with years of practice, and they assume every bed produces twice a year. The large figures include grain, oil, pasture for animals and the ground lost to paths, sheds and failures.

Neither figure includes the year the blight arrives, the fortnight you are away in August, or the fact that nobody wants to eat potatoes at every meal. Treat any single number you are given as a claim to check, not an answer.

Three very different goals

Supplementing your shopping is the first level. Around 50 square metres of well worked beds gives a household most of its salad, herbs, summer fruiting vegetables and some roots for perhaps six months a year. It cuts a food bill and it is genuinely achievable in a first season.

Feeding a household through a season is the second. Roughly 150 to 250 square metres per person, planted heavily with potatoes, squash, roots and brassicas, covers most of what you eat from July to January.

True year round independence is the third, and it is a different animal: 400 to 1000 square metres per person once you count grain, beans, oil, fruit trees and land that is resting. Most people who claim the first are quietly doing the second.

Doing the sum for your own plot

Work an example. A bed of 10 square metres of potatoes gives about 35 kg, roughly 27000 calories, which is eleven days of one adult. To carry one adult for a year on potatoes alone you would need about 300 square metres and you would still have no fat, no protein worth the name and nothing to eat in May.

Now do it with a mix. Potatoes, winter squash, parsnips and dry beans together average roughly 1500 to 2000 calories per square metre once paths and failures are counted. Divide 800000 by 1750 and you get about 460 square metres per adult for a full year of staples.

That is the honest figure to plan against.

What the numbers leave out

Ground is only half of it. Water in a dry summer, storage space that stays cool, and time in the two or three weeks of the year when everything must be planted or lifted at once are the limits that stop most people, not area.

Assume you will lose 20 to 30 percent of a planned harvest in a normal year to weather, pests and mistakes, and plan the extra ground in from the start rather than being shocked by it. Assume too that your first two seasons will produce well under half of what the tables predict.

None of this is a reason not to start. It is a reason to start small, measure what you actually harvest, and scale from real numbers.

Next lesson: Why Salad Does Not Feed You →

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