# How many mice are on the Earth?

We are 7 billion human beings on the Earth. But how many mice are there? How would you estimate such a number?

• There are many rats and mice in the world. From the recent number factors, in some LEDC's the population of mice are slowly rising at 1 mice every 15 seconds being born but in higly developed countries with great ecological systems, there is a complete difference with an unknown amount of rats and mice being born.
– user16842
Jul 19, 2015 at 21:50

Mark-recapture is the most frequently used method for small mammals. It's best when combined with uncertainty estimates and population dynamics models (e.g. projection matrix).

The fluctuations of small rodent populations have long fascinated scientists, and various models have been developed. Logistic regression models can be used to estimate likelihood of mice outbreak based on local rainfall data.

Estimates vary.

Rat population in New York city, for example, was thought to be 1 rat to 15 humans in the mid 40s, 1:36 in the late 40s (Davis ratio), 12:1 in 2002.

The population of mice is often estimated per hectare - 0.25-60/ha in buildings and 1-200 in the field, over 1000/ha during outbreaks. 10^9-10^10 hectares of habitable land means that populations of mice and men are, probably, of the same order of magnitude.

• "Rat population in New York city, for example, was thought to be 1 rat to 15 humans in the mid 40s, 1:36 in the late 40s (Davis ratio), 12:1 in 2002. " - why the reverse? Apr 1, 2012 at 14:59
• Can you try to extrapolate a very approximate world population from these numbers? Mar 31, 2016 at 19:00
• Good answer! Citations would be nice - eg. who's Davis? Mar 31, 2016 at 20:24