BoxFill Calculator

Electrical Box Types & Sizes

Complete reference guide for electrical box types with volume specifications and dedicated fill calculators for each box size.

Electrical box sizes and dimensions chart

A standard 4" square metal box is 4" × 4" and comes in depths of 1-1/4", 1-1/2" and 2-1/8", which hold 18.0 / 21.0 / 30.3 cubic inches. A 4-11/16" square box in the same depths holds 25.5 / 29.5 / 42.0 cubic inches. Volume, not the outside dimensions, is what decides how many conductors fit under NEC 314.16, so the chart lists both.

BoxDimensionsVolume (cu in)MaterialMax 14 AWGMax 12 AWG
Round Pan Box 1/2" Deep4" Round x 1/2"4.0Metal21
Handy Box 1-1/2" Deep4" x 2-1/8" x 1-1/2"10.3Metal54
Handy Box 1-7/8" Deep4" x 2-1/8" x 1-7/8"13.0Metal65
FS Box Single Gang4" x 2" x 2"13.5Metal66
Single Gang Device Box 2-3/4" Deep3" x 2" x 2-3/4"14.0Metal76
Handy Box 2-1/8" Deep4" x 2-1/8" x 2-1/8"14.5Metal76
Octagon Box 1-1/2" Deep4" Octagon x 1-1/2"15.5Metal76
4" Octagon Box 1-1/2" Deep4" Octagon x 1-1/2"15.5Metal76
4" Square x 1-1/4" Deep4" x 4" x 1-1/4"18.0Metal98
Single Gang Device Box 18 cu.in.3" x 2" x 3-1/2"18.0Metal98
Single Gang Device Box 3-1/2" Deep3" x 2" x 3-1/2"18.0Metal98
FD Box Single Gang4" x 2" x 2-5/8"18.0Metal98
4" Square x 1-1/2" Deep4" x 4" x 1-1/2"21.0Metal109
Masonry Box 3-1/2" Deep3-3/4" x 4" x 3-1/2"21.0Metal109
Octagon Box 2-1/8" Deep4" Octagon x 2-1/8"21.5Metal109
FS Box 2-Gang4" x 4" x 2"24.0Metal1210
4-11/16" Square x 1-1/4" Deep4-11/16" x 4-11/16" x 1-1/4"25.5Metal1211
2-Gang Device Box 2-3/4" Deep4" x 3" x 2-3/4"28.0Metal1412
4-11/16" Square x 1-1/2" Deep4-11/16" x 4-11/16" x 1-1/2"29.5Metal1413
4" Square x 2-1/8" Deep4" x 4" x 2-1/8"30.3Metal1513
2-Gang Device Box 3-1/2" Deep4" x 3" x 3-1/2"36.0Metal1816
4-11/16" Square x 2-1/8" Deep4-11/16" x 4-11/16" x 2-1/8"42.0Metal2118
3-Gang Device Box 2-3/4" Deep5-5/8" x 3" x 2-3/4"42.0Metal2118
4-Gang Device Box 2-1/8" Deep7-1/4" x 3" x 2-1/8"50.0Metal2522
Old Work Box 1-Gang 14 cu.in.3" x 2" x 2-3/4"14.0PVC76
PVC Single Gang Box 18 cu.in.3" x 2-1/4" x 3-3/4"18.0PVC98
Old Work Box 1-Gang 18 cu.in.3" x 2" x 3-1/2"18.0PVC98
PVC Single Gang Box 20 cu.in.3" x 2-1/4" x 4"20.0PVC108
PVC Round Ceiling Box 20 cu.in.4" Round x 2-1/4"20.0PVC108
PVC Single Gang Box 22 cu.in.3" x 2-1/4" x 4-1/4"22.5PVC1110
PVC 2-Gang Box 32 cu.in.4" x 3-1/4" x 3"32.0PVC1614
Old Work Box 2-Gang 32 cu.in.4" x 3" x 3"32.0PVC1614
PVC 3-Gang Box 44 cu.in.5-3/4" x 3-1/4" x 3"44.0PVC2219
PVC 4-Gang Box 60 cu.in.7-1/2" x 3-1/4" x 3"60.0PVC3026

Volumes for metal boxes come from NEC Table 314.16(A); nonmetallic boxes must be marked with their own volume, so use the marked cubic inches on the box you hold. “Max” counts are for a bare box with one wire gauge and no devices, clamps or grounds (see the box fill chart for capacity by gauge). Confirm dimensions against the manufacturer's data sheet before ordering.

What size junction box do I need?

Add up the NEC 314.16 allowances, multiply by the volume of your largest wire, and choose a box with at least that many cubic inches. Each conductor that enters and is spliced or terminated counts once; all ground wires together count once; internal cable clamps count once; each device counts twice; and each type of support fitting counts once. The volume per allowance is 2.00 cu in (14 AWG), 2.25 (12 AWG) or 2.50 (10 AWG).

Example: four 12/2 cables with ground, all wires spliced, no devices or clamps = (8 conductors + 1 for the grounds) × 2.25 = 20.25 cu in. A 4" square × 1-1/2" box (21.0 cu in) is the smallest of the standard 4" junction boxes that holds it. Let the box fill calculator handle devices, fittings and mixed cases.

Junction box size by number of cables

Each row assumes N cables of two insulated conductors plus a ground (14/2, 12/2 or 10/2 with ground), all conductors spliced or terminated in the box, one wire gauge, and no devices or support fittings. The “with clamps” column adds the one allowance for internal cable clamps. Boxes are the smallest of the standard junction-style boxes listed on this page that meet the required volume.

14 AWG cables

CablesAllowances (no clamps)No clamps: fill → smallest boxWith clamps: fill → smallest box
24 + 1 ground = 510.0 cu in → Octagon Box 1-1/2" Deep (15.5 cu in) at 2 cu in per allowance12.0 cu in → Octagon Box 1-1/2" Deep (15.5 cu in) at 2 cu in per allowance
36 + 1 ground = 714.0 cu in → Octagon Box 1-1/2" Deep (15.5 cu in) at 2 cu in per allowance16.0 cu in → 4" Square x 1-1/4" Deep (18 cu in) at 2 cu in per allowance
48 + 1 ground = 918.0 cu in → 4" Square x 1-1/4" Deep (18 cu in) at 2 cu in per allowance20.0 cu in → 4" Square x 1-1/2" Deep (21 cu in) at 2 cu in per allowance
510 + 1 ground = 1122.0 cu in → 4-11/16" Square x 1-1/4" Deep (25.5 cu in) at 2 cu in per allowance24.0 cu in → 4-11/16" Square x 1-1/4" Deep (25.5 cu in) at 2 cu in per allowance
612 + 1 ground = 1326.0 cu in → 4-11/16" Square x 1-1/2" Deep (29.5 cu in) at 2 cu in per allowance28.0 cu in → 4-11/16" Square x 1-1/2" Deep (29.5 cu in) at 2 cu in per allowance

12 AWG cables

CablesAllowances (no clamps)No clamps: fill → smallest boxWith clamps: fill → smallest box
24 + 1 ground = 511.25 cu in → Octagon Box 1-1/2" Deep (15.5 cu in) at 2.25 cu in per allowance13.5 cu in → Octagon Box 1-1/2" Deep (15.5 cu in) at 2.25 cu in per allowance
36 + 1 ground = 715.75 cu in → 4" Square x 1-1/4" Deep (18 cu in) at 2.25 cu in per allowance18.0 cu in → 4" Square x 1-1/4" Deep (18 cu in) at 2.25 cu in per allowance
48 + 1 ground = 920.25 cu in → 4" Square x 1-1/2" Deep (21 cu in) at 2.25 cu in per allowance22.5 cu in → 4-11/16" Square x 1-1/4" Deep (25.5 cu in) at 2.25 cu in per allowance
510 + 1 ground = 1124.75 cu in → 4-11/16" Square x 1-1/4" Deep (25.5 cu in) at 2.25 cu in per allowance27.0 cu in → 4-11/16" Square x 1-1/2" Deep (29.5 cu in) at 2.25 cu in per allowance
612 + 1 ground = 1329.25 cu in → 4-11/16" Square x 1-1/2" Deep (29.5 cu in) at 2.25 cu in per allowance31.5 cu in → 4-11/16" Square x 2-1/8" Deep (42 cu in) at 2.25 cu in per allowance

10 AWG cables

CablesAllowances (no clamps)No clamps: fill → smallest boxWith clamps: fill → smallest box
24 + 1 ground = 512.5 cu in → Octagon Box 1-1/2" Deep (15.5 cu in) at 2.5 cu in per allowance15.0 cu in → Octagon Box 1-1/2" Deep (15.5 cu in) at 2.5 cu in per allowance
36 + 1 ground = 717.5 cu in → 4" Square x 1-1/4" Deep (18 cu in) at 2.5 cu in per allowance20.0 cu in → 4" Square x 1-1/2" Deep (21 cu in) at 2.5 cu in per allowance
48 + 1 ground = 922.5 cu in → 4-11/16" Square x 1-1/4" Deep (25.5 cu in) at 2.5 cu in per allowance25.0 cu in → 4-11/16" Square x 1-1/4" Deep (25.5 cu in) at 2.5 cu in per allowance
510 + 1 ground = 1127.5 cu in → 4-11/16" Square x 1-1/2" Deep (29.5 cu in) at 2.5 cu in per allowance30.0 cu in → 4" Square x 2-1/8" Deep (30.3 cu in) at 2.5 cu in per allowance
612 + 1 ground = 1332.5 cu in → 4-11/16" Square x 2-1/8" Deep (42 cu in) at 2.5 cu in per allowance35.0 cu in → 4-11/16" Square x 2-1/8" Deep (42 cu in) at 2.5 cu in per allowance

Figures are computed with the same NEC 314.16 formula as the calculator, so they cannot drift from it. If your box has devices, fixtures or mixed wire sizes, use the calculator; for the counting rules (unbroken conductors, jumpers, looped wires) see the NEC 314.16 reference, and for capacity by box and gauge see the box fill chart.

Marked volume: standard metal boxes use the Table 314.16(A) volumes above, but nonmetallic boxes and boxes not in the table must be marked by the manufacturer with their volume (NEC 314.16(A)(2)). For those, use the marked cubic inches, not a table value. This page is a sizing aid, not a code opinion: check the edition and local amendments your inspector enforces.

All box types and volumes

34

Box Types

24

Metal Boxes

10

PVC Boxes

Metal Electrical Boxes

4" Square x 1-1/4" Deep

4" x 4" x 1-1/4"

18 cu.in.Max 9 x 14AWG

4" Square x 1-1/2" Deep

4" x 4" x 1-1/2"

21 cu.in.Max 10 x 14AWG

4" Square x 2-1/8" Deep

4" x 4" x 2-1/8"

30.3 cu.in.Max 15 x 14AWG

4-11/16" Square x 1-1/4" Deep

4-11/16" x 4-11/16" x 1-1/4"

25.5 cu.in.Max 12 x 14AWG

4-11/16" Square x 1-1/2" Deep

4-11/16" x 4-11/16" x 1-1/2"

29.5 cu.in.Max 14 x 14AWG

4-11/16" Square x 2-1/8" Deep

4-11/16" x 4-11/16" x 2-1/8"

42 cu.in.Max 21 x 14AWG

Octagon Box 1-1/2" Deep

4" Octagon x 1-1/2"

15.5 cu.in.Max 7 x 14AWG

4" Octagon Box 1-1/2" Deep

4" Octagon x 1-1/2"

15.5 cu.in.Max 7 x 14AWG

Octagon Box 2-1/8" Deep

4" Octagon x 2-1/8"

21.5 cu.in.Max 10 x 14AWG

Single Gang Device Box 2-3/4" Deep

3" x 2" x 2-3/4"

14 cu.in.Max 7 x 14AWG

Single Gang Device Box 18 cu.in.

3" x 2" x 3-1/2"

18 cu.in.Max 9 x 14AWG

Single Gang Device Box 3-1/2" Deep

3" x 2" x 3-1/2"

18 cu.in.Max 9 x 14AWG

2-Gang Device Box 2-3/4" Deep

4" x 3" x 2-3/4"

28 cu.in.Max 14 x 14AWG

2-Gang Device Box 3-1/2" Deep

4" x 3" x 3-1/2"

36 cu.in.Max 18 x 14AWG

3-Gang Device Box 2-3/4" Deep

5-5/8" x 3" x 2-3/4"

42 cu.in.Max 21 x 14AWG

4-Gang Device Box 2-1/8" Deep

7-1/4" x 3" x 2-1/8"

50 cu.in.Max 25 x 14AWG

Handy Box 1-1/2" Deep

4" x 2-1/8" x 1-1/2"

10.3 cu.in.Max 5 x 14AWG

Handy Box 1-7/8" Deep

4" x 2-1/8" x 1-7/8"

13 cu.in.Max 6 x 14AWG

Handy Box 2-1/8" Deep

4" x 2-1/8" x 2-1/8"

14.5 cu.in.Max 7 x 14AWG

Masonry Box 3-1/2" Deep

3-3/4" x 4" x 3-1/2"

21 cu.in.Max 10 x 14AWG

FS Box Single Gang

4" x 2" x 2"

13.5 cu.in.Max 6 x 14AWG

FD Box Single Gang

4" x 2" x 2-5/8"

18 cu.in.Max 9 x 14AWG

FS Box 2-Gang

4" x 4" x 2"

24 cu.in.Max 12 x 14AWG

Round Pan Box 1/2" Deep

4" Round x 1/2"

4 cu.in.Max 2 x 14AWG

PVC Electrical Boxes

PVC Single Gang Box 18 cu.in.

3" x 2-1/4" x 3-3/4"

18 cu.in.Max 9 x 14AWG

PVC Single Gang Box 20 cu.in.

3" x 2-1/4" x 4"

20 cu.in.Max 10 x 14AWG

PVC Single Gang Box 22 cu.in.

3" x 2-1/4" x 4-1/4"

22.5 cu.in.Max 11 x 14AWG

PVC 2-Gang Box 32 cu.in.

4" x 3-1/4" x 3"

32 cu.in.Max 16 x 14AWG

PVC 3-Gang Box 44 cu.in.

5-3/4" x 3-1/4" x 3"

44 cu.in.Max 22 x 14AWG

PVC 4-Gang Box 60 cu.in.

7-1/2" x 3-1/4" x 3"

60 cu.in.Max 30 x 14AWG

PVC Round Ceiling Box 20 cu.in.

4" Round x 2-1/4"

20 cu.in.Max 10 x 14AWG

Old Work Box 1-Gang 14 cu.in.

3" x 2" x 2-3/4"

14 cu.in.Max 7 x 14AWG

Old Work Box 1-Gang 18 cu.in.

3" x 2" x 3-1/2"

18 cu.in.Max 9 x 14AWG

Old Work Box 2-Gang 32 cu.in.

4" x 3" x 3"

32 cu.in.Max 16 x 14AWG