Metal Box Fill Capacities

NEC 2020 • 2023 COMPLIANT

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Maximum conductor counts for standard square, switch, and handy metal boxes.

Box Size (in)	Min. Vol (in³)	18 AWG	16 AWG	14 AWG	12 AWG	10 AWG	8 AWG	6 AWG
4 x 1-1/4 Round/Octagonal	12.5	8	7	6	5	5	4	2
4 x 1-1/2 Round/Octagonal	15.5	10	8	7	6	6	5	3
4 x 2-1/8 Round/Octagonal	21.5	14	12	10	9	8	7	4
4 x 1-1/4 Square	18.0	12	10	9	8	7	6	3
4 x 1-1/2 Square	21.0	14	12	10	9	8	7	4
4 x 2-1/8 Square	30.3	20	17	15	13	12	10	6
4-11/16 x 1-1/4 Square	25.5	17	14	12	11	10	8	5
4-11/16 x 1-1/2 Square	29.5	19	16	14	13	11	9	5
4-11/16 x 2-1/8 Square	42.0	28	24	21	18	16	14	8
3 x 2 x 1-1/2 Device	7.5	5	4	3	3	3	2	1
3 x 2 x 2 Device	10.0	6	5	5	4	4	3	2
3 x 2 x 2-1/4 Device	10.5	7	6	5	4	4	3	2
3 x 2 x 2-1/2 Device	12.5	8	7	6	5	5	4	2
3 x 2 x 2-3/4 Device	14.0	9	8	7	6	5	4	2
3 x 2 x 3-1/2 Device	18.0	12	10	9	8	7	6	3
4 x 2-1/8 x 1-1/2 Handy	10.3	6	5	5	4	4	3	2
4 x 2-1/8 x 1-7/8 Handy	13.0	8	7	6	5	5	4	2
4 x 2-1/8 x 2-1/8 Handy	14.5	9	8	7	6	5	4	2

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Related NEC Tables

Volume Allowances

Professional Usage Disclaimer

This data is provided for informational purposes only. Always verify with the latest edition of the National Electrical Code (NFPA 70) and consult with a licensed electrical professional or AHJ (Authority Having Jurisdiction) before performing any electrical work. Zing² is a reference tool, not a substitute for qualified engineering.

Professional Field Notes & Gotchas

▸Conductor Count: This table assumes NO devices (switches/outlets) or clamps. If you add these, you MUST use Table 314.16(B) to subtract volume.
▸Standard 4-Square: A 4 x 1-1/2 square box is the most common commercial box; it holds ten #12 wires theoretically, but in practice, you'll need an extension ring for more than six wires + a device.
▸Pigtails: Short pigtails (under 12 inches) that stay entirely within the box do NOT count toward your conductor volume calculation.
▸Mud Rings: Don't forget that mud rings and industrial covers add significantly to the available volume, which can save a 'failed' box fill inspection.

NEC 2023 vs 2026: What changed?

NEC 2023 vs 2026: No changes to the standard dimensions or counts. The 2026 code emphasized requirements for marking the volume on non-standard specialty boxes for clearer inspector verification.

Technical FAQs

How many #12 wires in a 4-square box?

A standard 4 x 1-1/2 square box can hold up to 9 #12 AWG conductors per Table 314.16(A). However, if you add an outlet, that count drops.

Does the ground wire count toward box fill?

Yes, but special rules apply. All grounding wires together count as only ONE volume allowance based on the largest ground present.

What is a 'Handy Box' capacity?

A standard 4 x 2-1/8 x 1-7/8 Handy Box has a 13.0 in³ capacity and can hold six #14 wires or five #12 wires (assuming no device).