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Box fill chart
NEC 2023 §314.16 — verify with your inspector (AHJ)
The volume each conductor takes in a box, how devices, clamps, fixture studs and grounds are counted, and the volumes of common metal boxes, from NEC 2023 §314.16.
Add up what goes in the box and compare it with the box's volume; plastic and other boxes are marked inside. Verify with your inspector (AHJ). The box fill calculator does the counting for you.
Verify with your local code and AHJ. Reference only, no warranty.
Volume per wire
| in³ | |
|---|---|
| 14 AWG | 2.00 |
| 12 AWG | 2.25 |
| 10 AWG | 2.50 |
| 8 AWG | 3.00 |
| 6 AWG | 5.00 |
What counts
| Each wire entering and spliced or landed | ×1 |
| Pigtail that stays in the box | ×0 |
| Internal cable clamps, all together | ×1 |
| Fixture stud or hickey, each kind | ×1 |
| Each device (switch, receptacle) | ×2 |
| Ground wires, first 4 together | ×1 |
| Each ground after 4 | + ×1/4 |
Clamps, studs, devices and grounds count at the largest wire.
Metal box volumes
| in³ | |
|---|---|
| Device box 3×2×2 | 10.0 |
| Device box 3×2×2½ | 12.5 |
| Octagon 4×1½ | 15.5 |
| Device box 3×2×3½ | 18.0 |
| Square 4×1½ | 21.0 |
| Octagon 4×2⅛ | 21.5 |
| Square 4¹¹⁄₁₆×1½ | 29.5 |
| Square 4×2⅛ | 30.3 |
| Square 4¹¹⁄₁₆×2⅛ | 42.0 |
Plastic and other boxes: use the volume marked inside.
Open the Box Fill calculatorOpen this sheet in the toolkit to search it, pin it and use it offline.
Questions
How many cubic inches per 14 AWG wire?
2.00 in³; 12 AWG is 2.25 in³ (NEC 2023 §314.16(B)).
How much does a device count?
Each device on a yoke or strap counts as two wires of the largest size connected to it.
What is the volume of a 4×2⅛ square box?
30.3 in³ for the metal box (NEC 2023 §314.16(A)).