Population

The term population referred to the total number of individuals inhabiting a certain location.

Total population
In 1791, Hempel noted the planet Earth's population to be "eight hundred million, give or take." (AUDIO: The Sword of the Chevalier)

In 2006, the Ninth Doctor claimed Earth's population to be five billion. (TV: World War Three)

Onboard the Titanic in 2008, the Tenth Doctor stated that the Earth's population was 6 billion. (TV: Voyage of the Dammed)

During the 456 crisis of 2009, Rick Yates acknowledged projections which predicted that Earth's population would reach nine billion by 2050, a two and a half billion rise. Soon after, Jack Harkness boasted that "over six billion angry human beings" would fight the 456. Denise Riley noted the Earth's population to be 6.7 billion people. (TV: Children of Earth: Day Four)

On Christmas Day 2009, a total of 6,727,949,338 people were temporarily transformed into the Master Race, constituting almost the entire human population of Earth save Donna Noble and Wilfred Mott, who were spared the transformation. (TV: The End of Time)

In 2010, 79B Aickman Road's autopilot noted that 17 potential pilots had been tried and that 6400000026 remained. Earlier that day, Sophie had estimated the total population at six billion. (TV: The Lodger)

In 2018, the Twelfth Doctor noted Earth's population to be seven billion. (TV: The Lie of the Land) In 2018 (TV: The Battle of Ranskoor Av Kolos) and early 2019, the Thirteenth Doctor approximated it at the same value. (TV: Resolution)

By the year 2472, Earth's population was 100 billion. (TV: Colony in Space)

In the year 200,000, the Ninth Doctor noted Earth's population as being 96 billion. (TV: The Long Game)

Specific locations
In 2007, Elton Pope claimed the population of London to be ten million. (TV: Love & Monsters)

In 2009, Rick Yates noted that the United Kingdom had a population of 61 million, which was projected to increase to 77 million by 2050. (TV: Children of Earth: Day Four)

In 2012, Henry van Statten noted Salt Lake City, the city nearest to his Vault, to have a population of one million. (TV: Dalek)

Other locations
At the time of its disappearance, Bandraginus V had a population of a thousand million. (TV: The Pirate Planet)

In the year 4000, the Solar System had a combined population of forty billion. (TV: The Daleks' Master Plan)

The City of the Saved was home to every human to ever live. The City's population was in the septillions and increased by 0.3 septillion each year. (PROSE: The Book of the War) The orientation material given to visitors of the City estimated the population was between 1024 and 1027 septillion, but the City census of AF 291 reported it was closer to 1038 septillion. (PROSE: Of the City of the Saved...)