World population is presently about seven billion people. That is a carefully done estimate by professional demographers so let us accept that as being accurate to within ten percent. There is no use asking for a more precise number even at present, and when estimating historical numbers an accuracy of half to double a given number may be overly optimistic.

What is proposed here is a an easy way to remember historical populations. This method is accurate enough to stay historically oriented to population. There are more precise numbers but they should be taken with caution especially when reflecting sudden changes, such as the plague of 1347, where the accuracy is even more suspect. Sometimes data presented will show mathematical precision which isn’t really there. For example, say there are about one hundred thousand people living in a city and about one third of them died in the plague. The quick and easy calculation, commonly seen will do something silly like: a town with a population of 100,000 is struck by plague which is reported to have killed a third of the people. So a precise calculation can be made by dividing the population by 3 which equals 33,333 died leaving a population of 66,667 living people. This is precise enough mathematically but is obvious nonsense in fact. The problem is that a precise number is used for the calculation which gives an exact number when others see this number they think it is accurate to the number stated and they use it to calculate other things. Thus, we sometimes see things which are treated as accurate but when checked into the data was soft and intended for general conclusions and thus any precision is totally suspect. Here is a wonderful site World Population Since Creation which plays lots of mathematical games, some of which are good some of which are “hopefully” intentionally hilarious.

Hoping not to fall into total nonsense there is presented below some reasonable estimates of world population. As you look over the chart notice how widely divergent these professional estimates are. In an effort to cut through the confusion I have been using a simple estimate to keep things in perspective. It isn’t intended to be precisely accurate but it is usually within the error ranges of professional demographers, and it has the advantage of being very easy to learn and to remember. Look over the chart and then look at my method below.

## Historical Estimates of World Population

(Population in millions as estimated by professional demographers. When lower and upper estimates are the same they are shown under their name which means “Lower.” For a more complete rendition of this chart a click through is at the bottom.)

This graph has my estimates inserted in bold type using a generalized formula, see below. This method is intended as a quick way of remembering approximate populations over the entire human historical period. The bolded data is not too distant from the population experts boundries for maximum and minimum for three thousand years. There may be authorities which would include any specific population estimated for a specified date. The formula requires only knowing that world population was near four billion in 1975 AD and 200 million at 1 AD. Going forward or backward from 1975 the population is doubles in fifty years by doubles, thus going back doubling the amount of years halves the population and that procedure is followed throughout the chart which included as bolded data above. The method gives a good guess back to 1,000 BC which may be as accurate as the population data permits. But it is easy to shift method slightly at 1AD with 200 million people and modifying the halving time at starting to 500 years rather than 50 as from 1975 that adjustment gives a fair estimate all the way back to the advent of agriculture. This concept is hard to describe but is easier to understand if you look over the list below. Set the boundary for these guess at +/- 20% or more.

2025 AD = 8 billion ( this added 50 years to to 1975 to double)

1975 AD = 4 billion remember this date and population ½ in -50 years =…

1925 AD = 2 billion (½ in -100years =…

1825 AD = 1 billion (½ in -200years =…

1625 AD = ½ billion (½ in -400years =…

1225 AD = ¼ billion (½ in -800 years =…

Shift the method a bit to 500 year for halving

1 AD = 200 million – remember this date and population (½ in -500 years =…

500 BC =100 million (½ in -500 years =…

1000 BC = 50 million (½ in -1,000 years =…

2000 BC – 25 million (½ in -2,000 years =…

4000 BC = 10 million (½ in -4,000 years =…

8000 BC = 5 million (½ in -8,000 years =…

16000 BC = 2.5 million

A good guess has a working central point with upper and lower boundaries.