What is the minimum length for a shotgun to be legally owned in Utah without requiring registration as a short-barreled shotgun?

In Utah, the minimum length for a shotgun to be legally owned without requiring registration as a short-barreled shotgun is 18 inches. This is in accordance with federal guidelines that define a shotgun with a barrel length of less than 18 inches as a short-barreled shotgun, which requires registration under the National Firearms Act. So, in order to comply with Utah gun laws and avoid the need for registration, the shotgun must have a barrel length of at least 18 inches. The other options are incorrect because they do not correspond to the specific minimum length requirement set for shotguns in Utah.