So one of the perennial questions that plagues my campaign planning is as follows: “How much space does a tribe of goblins need to be self sufficient? Can I place them in this forest and that’s good enough? Is there also room for these gnolls?”

Now yes, as GM I can do whatever I like, and NO no player has EVER called me on having unrealistic population densities. This is more of a personal guideline thing: knowing what’s realistic or historical helps me make decisions. So, I recently sat down and did some research. Here’s what I came up with:

Units:

Acres: An acre (ac) is a unit of area 22 yards by 220 yards. It was historically defined as the area that can be plowed in one day with a yoke of oxen. There are 640 acres in a square mile. Few countries still use the acre, but they’re big ones that include most of our readership, so we’ll include it here.

Hectare: For most of the world, area is measured using the metric system. Though not an “official’ measurement the hectare (ha), a square hectometer, 100m by 100m is commonly used for metric land measurement.

Unit Months: The measurements below are given in acre months and hectare months which as far as I know aren’t a standard unit, but which I define as the given amount of land used for a month.

Rates:

Modern Agriculture: In our current system, depending on machinery, irrigation and chemical assistance, abundant land produces enough food to feed a person for a year given 8 ac months or 3 ha months.

Medieval Agriculture: Historically agriculture was much less productive. Farming using animal assistance and no chemical intervention on abundant land produces enough food to feed a person for a year given 40 ac months or 16 ha months.

Hunter-Gatherer: The amount of abundant land required to support a single person with a hunter-gatherer agriculture is approximately 3000 ac months or 1200 ha months. However, unlike farming systems which are mostly efficient, hunter gatherer systems are naturally inefficient systems which means they don’t follow a linear production pattern. Thus, when determining the area needed to support X people you don’t multiply by X, but instead by X.75. This is because the more people hunting/gathering the more efficiently they do it. Thus, for example, 1000 people count only as 1000.75 = 180 people due to these increases in efficiency. In theory, these increases would eventually lead to a system just as efficient as agriculture, but that happens well outside the scale we’re concerned with.

Other Considerations:

Growing season: Because the rates above are in ac months or ha months, dividing the rate by the number of months in the growing season will convert them to ac years and ha years. Because the measurements are the amount of land needed per person per year, this conversion gives you a simple amount of land required per person.

Mass: The rates above are for supporting human sized beings. Food requirements roughly scale by mass, so creatures with half the mass of humans need half the land, while those twice the size need twice the land and so forth.

Unequal production distribution: Especially in large farming societies not all land is worked equally nor is it all of the same quality. While you’re certainly able to break the land into chunks and work out the population each will support and make sure the total population and the total support match, another valid approach would be to multiply the rate by the proportion of land used.

Land quality: Not every culture in your game world lives in the American breadbasket or medieval France where these optimum rates come from. If your setting is less productive feel free to adjust the rates downwards by dividing by a proportion (for example, .5 for half optimum or .8 for 80%). Similarly, if your setting is more productive, through the use of magic, more advanced technology, etc… adjust them upwards by dividing by 1 + a proportion (for example 1.15 for 15% above optimal).

Other Forms of income: Plenty of cultures supplement their food production via other methods, primarily trade or raiding. In these cases you can assume a culture supplements their production with some of their neighbor’s excess production and adjust the numbers by multiplying by the proportion of resources that are produced internally. Of course nearby cultures with no excess production are of no use or will quickly starve. These sorts of cultures are classic adventure hooks for your game. Protect the caravan! Stop the raids!

Formulae:

For determining the amount of land required by a group of size X you would use this formula:

for farmers:

(average rate/growing season) * (1/land quality) * population * relative mass * domestic production = land required

for hunter/gatherers:

(average rate/growing season) * (1/land quality) * population.75 * relative mass * domestic production = land required

Conversely, for determining the amount of people who can comfortably be supported by a parcel of land you would use these formulae:

for farmers:

land available / [(average rate/growing season) * (1/land quality) * relative mass * domestic production] = supportable population

for hunter/gatherers: