Gauge-Caliber Conversion Table 

Caliber is the decimal-inch diameter of the gun barrel.  For example the land to land diameter of a 54 caliber rifle is 54/100's of an inch.  

The gauge of a gun is the measurement of the bore of the gun in terms of the number of lead balls of the same diameter that would weigh a pound.   For example a 20 gauge Northwest Trade gun would require balls of a size such that 20 balls would weigh one pound.  

In those times, a man was much more likely to refer to the bore diameter of his gun in terms of balls per pound than in gauge or caliber.  "The rifle I use when I hunt large game shoots 30 balls per pound."

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