Given: 3 size 12 AWG, two-conductor-with-ground type NM cables are spliced in a ceiling junction box that has internal cable clamps and flat cover. What is the minimum trade size metal octagonal box that may be used?

Given: 3 size 12 AWG, two-conductor-with-ground type NM cables are spliced in a ceiling junction box that has internal cable clamps and flat cover. What is the minimum trade size metal octagonal box that may be used?