Free tool · Texas journeyman calculations · no sign-up

Box fill calculator and exam trainer

Tell it what is in the box. It counts every conductor, clamp, device and grounding conductor the way the exam does, shows the working, and points to the item people forget. Then practice exam-style questions below.

Built on the 2026 NEC counting method in 314.16. On the Texas exam you get about 4 min 14 s per Calculations question; a box fill question should take you half that.

What is in the box?

Box fill = Σ (allowances × in³ for that size)

Size (AWG)Ending or splicedPassing throughLooped 12 in+ 14 12 10

Grounding conductors (how many) Largest grounding conductor Devices on yokes (how many) Largest conductor connected to them Second device group (how many) Largest conductor connected to them Luminaire stud or hickey types Pigtails that never leave the box Internal cable clamps Devices are 2 gangs wide Box volume (in³, marked or from your book) Marked ring or extension (in³)

Volumes per conductor size are the ones in 314.16 of the 2026 NEC. Use the volume marked on the box when there is one. Equipment grounding conductors beyond four add 1/4 each.

Try it like the exam

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New question every time. Answer, see the working, and watch your streak.

Ready for the whole Calculations portion?

Box fill is one of the question types on the Texas Calculations portion. Our free 20-question diagnostic covers all of them on the 2026 NEC and shows which areas cost you points.

Take the free diagnostic See the full exam pack

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