Is there a List of gun calibers smallest to largest?

Paintball guns (or "markers") are typically .68 caliber (17 mm). The following table lists some commonly used calibers where both metric and imperial are used as equivalents. Due to variations in naming conventions, and the whims of the cartridge manufacturers, bullet diameters can vary widely from the diameter implied by the name.

For example, there is a difference of as much as 0.045 inches (6.358 mm) between the smallest and largest of the several cartridges designated as '.38 caliber'. And it may be noted that .38 inches is more than 9 1/2 mm. Shotguns are classed according to gauge, a related expression.

The gauge of a shotgun refers to how many lead spheres the diameter of the bore would equal a pound. In the case of a 12-gauge shotgun, it would take twelve spheres the size of the shotgun's bore to equal a pound. A numerically larger gauge indicates a smaller barrel: a 20-gauge shotgun requires more spheres to equal a pound; therefore, its barrel is smaller than the 12 gauge.

This metric is used in Russia as "caliber number": e.g. , "shotgun of the twelve caliber." The sixteenth caliber is known as "lordly" (Russian:?). While shotgun bores can be expressed in calibers (the .410 bore shotgun is in fact a caliber measure of .41 caliber 11 mm), the nature of shotshells is such that the barrel diameter often varies significantly down the length of the shotgun barrel, with various levels of choke and backboring.

The length of artillery barrels has often been described in terms of multiples of the bore diameter e.g. A 4-inch gun of 50 calibers would have a barrel 50 x 4 inches = 200 inches long. Smoothbore cannon and carronade bores are designated by the weight in Imperial pounds of round solid iron shot of diameter to fit the bore. Standard sizes are 6, 12, 18, 24, 32 and 42 pounds, with some 68 pound weapons, and other nonstandard weapons using the same scheme.

From about the middle of the 17th century until the middle of the 19th century, measurement of the bore of large gunpowder weapons was usually expressed as the weight of its iron shot in pounds. Iron shot was used as the standard reference because iron was the most common material used for artillery ammunition during that period and solid spherical shot the most common form encountered. Artillery was classified thereby into standard categories, with 3 pounders (pdr.), 4 pdr., 6 pdr., 8 pdr., 9 pdr, 12 pdr, 18 pdr., 24 pdr. and 32 pdr. being the most common sizes encountered; although larger, smaller and intermediate sizes existed.

However, in practice there was significant variation in the actual mass of the projectile for a given nominal shot weight. The country of manufacture is a significant consideration when determining bore diameters. For example, the French livre, until 1812, had a mass of 489.5 g whilst the contemporary English (Avoirdupois) pound massed approximately 454 g.