How short can you cut off a shotgun?

In the United States, the minimum legal length for a shotgun barrel is 18 inches, and the overall length of the shotgun must be at least 26 inches. Cutting a shotgun barrel shorter than 18 inches or modifying it in a way that results in an overall length of less than 26 inches can classify it as a short-barreled shotgun, which requires special registration under the National Firearms Act. Always check local laws and regulations, as they can vary significantly by state or locality.