NEC Box Fill Chart — Table 314.16 Metal Boxes & Volume

Size of Conductor (AWG)	cm3	in.3
18	24.6	1.50
16	28.7	1.75
14	32.8	2.00
12	36.9	2.25
10	41.0	2.50
8	49.2	3.00
6	81.9	5.00

Size of Conductor (AWG)

cm3

in.3

24.6

1.50

28.7

1.75

32.8

2.00

36.9

2.25

41.0

2.50

49.2

3.00

81.9

5.00

Metal box capacities — 314.16(A)

Box Trade Size			Minimum Volume		Maximum Number of Conductors*(arranged by AWG size)
mm	in.	Shape	cm3	in.3	18	16	14	12	10	8	6
100 × 32	(4 × 114)	round/octagonal	205	12.5	8	7	6	5	5	4	2
100 × 38	(4 × 112)	round/octagonal	254	15.5	10	8	7	6	6	5	3
100 × 54	(4 × 218)	round/octagonal	353	21.5	14	12	10	9	8	7	4
100 × 32	(4× 114)	square	295	18.0	12	10	9	8	7	6	3
100 × 38	(4 × 112)	square	344	21.0	14	12	10	9	8	7	4
100 × 54	(4 × 218)	square	497	30.3	20	17	15	13	12	10	6
120 × 32	(41116 × 114)	square	418	25.5	17	14	12	11	10	8	5
120 × 38	(41116 × 112)	square	484	29.5	19	16	14	13	11	9	5
120 × 54	(41116 × 218)	square	689	42.0	28	24	21	18	16	14	8
75 × 50 × 38	(3 × 2 × 112)	device	123	7.5	5	4	3	3	3	2	1
75 × 50 × 50	(3 × 2 × 2)	device	164	10.0	6	5	5	4	4	3	2
75× 50 × 57	(3× 2 × 214)	device	172	10.5	7	6	5	4	4	3	2
75 × 50 × 65	(3 × 2 × 212)	device	205	12.5	8	7	6	5	5	4	2
75 × 50 × 70	(3 × 2 × 234)	device	230	14.0	9	8	7	6	5	4	2
75 × 50 × 90	(3 × 2 × 312)	device	295	18.0	12	10	9	8	7	6	3
100 × 54 × 38	(4 × 218 × 112)	device	169	10.3	6	5	5	4	4	3	2
100 × 54 × 48	(4 × 218 × 178)	device	213	13.0	8	7	6	5	5	4	2
100 × 54 × 54	(4 × 218 × 218)	device	238	14.5	9	8	7	6	5	4	2
95 × 50 × 65	(334 × 2 × 212)	masonry box/gang	230	14.0	9	8	7	6	5	4	2
95 × 50 × 90	(334 × 2 × 312)	masonry box/gang	344	21.0	14	12	10	9	8	7	4
min. 44.5 depth	FS — single cover/gang (134)		221	13.5	9	7	6	6	5	4	2
min. 60.3 depth	FD — single cover/gang (238)		295	18.0	12	10	9	8	7	6	3
min. 44.5 depth	FS — multiple cover/gang (134)		295	18.0	12	10	9	8	7	6	3
min. 60.3 depth	FD — multiple cover/gang (238)		395	24.0	16	13	12	10	9	8	4

Notes that change the answer — 314.16(A)(2)

*Where no volume allowances are required by 314.16(B)(2) through (B)(6).

Race your codebook — 3 lookups on this table

A field-installed cover screw on a device box will penetrate into the wiring space. Per the general rule for such fasteners, which section limits how far a cover-attaching screw may extend into the box?

A 314.5
B 314.4
C 314.16(B)(2)
D 314.17(B)(4)

Show answer & explanation

Correct: A — 314.5

314.5 sets the field-installed fastener limits, including that cover-attaching screws extend no more than 10 mm (3/8 in.) into the box. 314.16(B)(2) instead addresses fill allowance for internal clamps, not fastener penetration depth.

An electrician is installing a self-tapping screw through the sidewall of a 50 in.3 nonmetallic device box to secure internal equipment, not related to a cover or a clamp covered elsewhere. Which section dictates how flush that fastener tip must be inside a box this size?

A 314.3
B 314.16(A)(1)
C 314.17(A)
D 314.5

Show answer & explanation

Correct: D — 314.5

314.5(6) requires fasteners penetrating the wall of a box not exceeding 100 in.3 to be made flush with the box interior, so 314.5 governs. 314.16(A)(1) instead covers box volume calculation for standard boxes, not fastener protrusion.

You're wiring a standard single-gang device box with two 12/2 NM cables, one internal cable clamp, and a duplex receptacle. Which section provides the box fill calculation methodology (conductor fill, clamp fill, and device fill allowances) needed to determine if the box is large enough?

A 314.16(A)
B 314.17(B)
C 314.16(B)
D 314.19

Show answer & explanation

Correct: C — 314.16(B)

314.16(B) is the Box Fill Calculations section that lists the conductor, clamp, support fitting, device, EGC, and terminal block fill allowances used to total up required volume. 314.16(A) instead covers how to determine the box's own volume (standard vs. other boxes), which is a different step in the same overall calculation.

Table 314.16 — box fill

Volume per conductor — 314.16(B)

Metal box capacities — 314.16(A)

Race your codebook — 3 lookups on this table

Every table. Timed lookups. Spaced repetition.

Table 314.16 — box fill

Volume per conductor — 314.16(B)

Metal box capacities — 314.16(A)

Race your codebook — 3 lookups on this table

Keep going

Every table. Timed lookups. Spaced repetition.