How do you calculate the speed of a bullet?

Bullets are fired at differents velocities. Generally longer barreled firearms fire bullets at higher velocities. The highest velocities among commonly used weapons were probably achieved by World War II era anti-tank rifles. German PzB 38 could fire bullets at 1210 meters per second.

As was said up there- depends on the bullet. A light loaded .45 pistol might be 900 feet per second, and a fast rifle bullet may be 4,500 feet per second.