Most of the world’s firearms are privately owned. In 2007 the Small Arms Survey estimated that civilians owned some 650 million of the world’s firearms, with armed forces owning around 200 million, and 26 million in the hands of law enforcement.

With the world’s factories delivering millions of newly manufactured firearms annually—far outnumbering those being destroyed—civilian ownership is growing in most countries. The highest national rate of civilian firearm ownership is in the United States, with at least 90 firearms per every 100 people.

Estimating Civilian Owned Firearms, a new Research Note from the Small Arms Survey, provides an overview of how these estimates are reached, and the challenges of gathering information about civilian possession of arms.

Differences in national gun culture —each country’s unique combination of historic and current sources of supply, laws and attitudes toward firearms ownership—often have distinct effects on the classification, ownership and perception of firearms, and this complicates the calculation of international figures.

Given the impossibility of being sure of the total number of all guns, total figures rely on estimation. Country assessments rely on the combination of a range of sources and tools, using as many different methods as possible. These include: gun registration; expert estimates; household surveys; proxy indicators (such as gross domestic product per capita, and firearm suicides); and analogous comparison (ie. comparison to similar but better-understood countries).

The Research Note explains that while these figures are not accurate or complete, it remains important to continue to seek the best possible estimates while acknowledging their limitations.