In angle pulls, conduits enter and exit from adjacent sides of the pull box. Formula: Box Width/Height = 6 × D Where D = Diameter of the largest conduitA junction box sizing calculator is an indispensable tool for electricians and DIY enthusiasts to quickly determine the correct physical dimensions and volume requirements of electrical enclosures. Maintaining sufficient physical space inside junction boxes is a critical aspect of electrical. Article Summary: Calculating the correct junction box size per the NEC 2023 involves a process known as a “box fill calculation,” primarily governed by NEC Article 314. The first step is to determine the total number of conductor equivalents in the box.