The FBI estimates that there are over 200 million privately-owned firearms in the US. If you add those owned by the military, law enforcement agencies and museums, there is probably about 1 gun per person in the country.

If you want to get a rough idea of how many guns there are out there just look at how many people you see out there then multiply by a factor of estimated ownership. The last best guess was about 350,000,000 Total. That would be 1 weapon for every man woman and child. The average gun enthusiast owns several firearms which includes pistols, shotguns, and rifles of all makes and models. It is often estimated that about 1 in 4 people own any firearms and on average firearms owners own 4 guns each.

No one knows the exact number of firearms owned by private citizens in the US, In 1995, the BATFE estimated that there were about 223 million firearms owned by individuals in the US. The number has increased since then.

There is no definitive answer, because most states don't require registration.

The Small Arms Survey in 2007 by the Graduate Institute of International Studies in Geneva estimated 270 million firearms in the US.

There have been 156,577,620 gun registry applications submitted to the National Firearms Administration (NFA) from Nov 1998 to Nov 2012.