Key Takeaway: A standard single-gang box measures 2. 75 inches, but depth varies from 1. Professional installation requires precise adherence to NEC (National Electrical Code) volume standards. This guide explains typical wall-mount and floor-standing dimensions, how to read catalog sizes, and how to choose the right enclosure size for your layout. Do Standard Electrical Enclosure Sizes. Choosing the correct electrical box dimensions is essential for safe wiring, code compliance, and long-term reliability. Choosing the proper enclosure requires fluency in the language of gangs, physical footprint, and—most importantly— internal. How wide is a 2-gang electrical box? The measurements of a standard single-gang device electrical box are typically 2 ¼ inches wide, 3 ¾ inches high, and 2 ½ to 3 ½ inches deep. Picking the right size matters. If the box is too small, things can get hot or hard to fix.