FIG. 01 — BOX FILL REFERENCE
NEC 314.16(B) Box Fill Chart
Per-conductor cubic-inch allowances from NEC Table 314.16(B), and the maximum conductor count each standard metal box accepts (conductors only — clamps, yokes, EGCs and supports add their own allowances on top).
FIG. 02
PER-CONDUCTOR VOLUME ALLOWANCE
NEC 2023 Table 314.16(B) — Cubic inches per conductor by AWG.
| Conductor size (AWG) | Volume allowance (in³) |
|---|---|
| #18 | 1.50 |
| #16 | 1.75 |
| #14 | 2.00 |
| #12 | 2.25 |
| #10 | 2.50 |
| #8 | 3.00 |
| #6 | 5.00 |
FIG. 03
MAX CONDUCTORS PER STANDARD METAL BOX
Conductor-only count. Add allowances for clamps (1×), yokes (2×), EGC (1×) and supports (1×) — all in the largest AWG entering the box.
| Box (NEC 314.16(A)) | in³ | #18 | #16 | #14 | #12 | #10 | #8 | #6 |
|---|---|---|---|---|---|---|---|---|
| 4" × 1-1/4" square | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 |
| 4" × 1-1/2" square | 21.0 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 4" × 2-1/8" square | 30.3 | 20 | 17 | 15 | 13 | 12 | 10 | 6 |
| 4-11/16" × 1-1/4" square | 25.5 | 17 | 14 | 12 | 11 | 10 | 8 | 5 |
| 4-11/16" × 1-1/2" square | 29.5 | 19 | 16 | 14 | 13 | 11 | 9 | 5 |
| 4-11/16" × 2-1/8" square | 42.0 | 28 | 24 | 21 | 18 | 16 | 14 | 8 |
| 3" × 2" × 2" device | 10.0 | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 3" × 2" × 2-1/2" device | 12.5 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 3" × 2" × 2-3/4" device | 14.0 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 3" × 2" × 3-1/2" device | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 |
| 4" × 2-1/8" × 1-1/2" device | 10.3 | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 4" × 2-1/8" × 1-7/8" device | 13.0 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 4" × 2-1/8" × 2-1/8" device | 14.5 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 3-1/2" octagonal × 1-1/2" | 12.5 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 4" octagonal × 1-1/2" | 15.5 | 10 | 8 | 7 | 6 | 6 | 5 | 3 |
| 4" octagonal × 2-1/8" | 21.5 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
FIG. 04
FREQUENTLY ASKED QUESTIONS
NEC Table 314.16(B) lists fixed cubic-inch allowances per conductor AWG, derived from typical insulated-conductor diameters plus working clearance: #14 = 2.0 in³, #12 = 2.25 in³, #10 = 2.5 in³, #8 = 3.0 in³, #6 = 5.0 in³. These values are used regardless of insulation type because box fill is about physical room to bend and terminate, not heat dissipation.