Abstract: A firearm measuring device for measuring all external dimensions of a firearm is comprised of an elongated rectangular caliper body member having measurement indicia inscribed thereon. A pair of jaws affixed on the caliper body member, one jaw affixed to a carriage and moveable along the caliper body member, a second jaw permanently affixed at one end of the caliper body member. A drop meter affixed to the caliper body member adjacent to the fixed jaw and vertically adjustable along the length of the drop meter by a channel within the length of the drop meter. The drop meter having a measurement indicia inscribed thereon. An extension member for attachment to the caliper body member having a bottom tooth-shaped configuration which is positioned on a gun barrel. The extension member having a magnetic means recessed within the extension member for securing the extension member in combination with the caliper body to the gun barrel eliminating need of holding the device during operation.