NEC Box Fill & Conduit Fill Calculator

Step 1 — Select Box

Box Type (Table 314.16(A))

Step 2 — Conductors Entering the Box

Each conductor that passes through or terminates in the box counts as 1 unit per 314.16(B)(1). Count only current-carrying conductors and EGCs — do NOT count conductors that originate and terminate entirely within the box (e.g., pigtails ≤ 6 in that do not pass through a knockout).

AWG Size	Qty

Step 3 — Deductions / Additional Fill Items

314.16(B) requires additional fill for the following. AWG size fields below refer to the largest conductor associated with that item.

Internal Cable Clamps? (314.16(B)(2))

Largest Conductor at Clamps (AWG)

Devices / Yokes (e.g., receptacles, switches) (314.16(B)(4))

Largest Conductor at Device(s) (AWG)

Equipment Grounding Conductors (EGCs) (314.16(B)(5))

Largest EGC in Box (AWG)

Equipment Bonding Jumpers (EBJs) in Box (314.16(B)(5))

Largest EBJ (AWG)

Step 1 — Select Raceway

Raceway Type

Trade Size

Step 2 — Conductors

Add one row per conductor group (same type, size, and insulation). Conductor areas from Chapter 9 Table 5.

Insulation	AWG / kcmil	Qty

Study aid only — Verify against the adopted code edition / a licensed professional before use in real project/estimate documentation. All conductor and raceway data is from NEC 2023 Chapter 9. Actual installed conditions (bends, conduit body types, conductor temperature ratings, etc.) may impose additional restrictions not covered here.