While nobody knows precise numbers, a good estimate is that there are 500 million firearms in circulation - approximately one for every twelve people in the world. And this 500 million includes at least 100 million assault rifles. According to the US Arms Control and Disarmament Agency (ACDA), small arms and ammunition represent about 13 percent of the total worldwide trade in conventional weapons. Using ACDA's estimate of $172 billion for total world arms exports in 1990-1995, this yields $22.2 billion worth of small arms sales, an enormous figure especially considering the low cost of small arms.
According to United Nations estimates there are about 10 million small arms and light weapons circulating in Afghanistan, about seven million in West Africa and two million in Central America. International trade in such weapons is estimated at $3 billion per year.