10 AWG Wire Box Fill
By Jack Shi, updated October 12, 2026
2.50
cu.in. per conductor
40.97
cm³ per conductor
30A
Max Ampacity
Common Applications
Maximum 10 AWG wires per box
All 34 box entries, sorted by volume. Each limit is floor(box volume / conductor allowance), before devices, internal clamps, grounds, or other fittings. Use the actual box marking for your installation.
In the 18.0 cu. in. 4" Square x 1-1/4" Deep, 8 conductors of 12 AWG fit versus 7 of 10 AWG: 1 fewer with the larger wire.
Worked examples: 30 A receptacles and splices
All insulated conductors and equipment grounds below are 10 AWG. Each device occupies a single yoke; all internal clamps share one allowance, and the grounds shown share one allowance based on the largest EGC. There are no fixture studs, hickeys, or terminal blocks, and no added cover or extension-ring volume. PASS and FAIL describe the box-fill calculation only.
A. 30 A, 240 V receptacle on one 10/3 NM-B cable with ground
Assume the receptacle requires all 3 insulated conductors: two hots and a neutral. Count 1 device, 1 internal cable-clamp allowance, and 1 grounding allowance. The device uses 2 conductor volumes.
conductors (3 × 2.50 = 7.50) + device (2 × 2.50 = 5.00) + internal clamps (1 × 2.50 = 2.50) + grounds (1 × 2.50 = 2.50) = 17.5 cu. in.
- 4" Square x 1-1/4" Deep (18.0 cu. in.): PASS, 97.2% fill (0.5 cu. in. spare).
- 4" Square x 1-1/2" Deep (21.0 cu. in.): PASS, 83.3% fill (3.5 cu. in. spare).
B. Splice junction of two 10/2 cables with ground
Count 4 insulated conductors, 0 devices, 1 internal clamp allowance, and 1 allowance for the grounds together. The splices add no device allowance.
conductors (4 × 2.50 = 10.00) + device (0 × 2.50 = 0.00) + internal clamps (1 × 2.50 = 2.50) + grounds (1 × 2.50 = 2.50) = 15.0 cu. in.
- 4" Octagon Box 1-1/2" Deep (15.5 cu. in.): PASS, 96.8% fill (0.5 cu. in. spare).
- 4" Square x 1-1/4" Deep (18.0 cu. in.): PASS, 83.3% fill (3.0 cu. in. spare).
C. A small single-gang device box
The 3" x 2" x 2-1/2" Device Box has 12.5 cu. in. With 1 device (5.0 cu. in.) and 1 grounding allowance (2.5 cu. in.), the remaining insulated-conductor limits are:
- Without an internal clamp: 2 conductors; 12.5 cu. in., 100.0% fill (PASS). Adding another conductor requires 15.0 cu. in. (FAIL).
- With an internal clamp: 1 conductor; 12.5 cu. in., 100.0% fill (PASS). Adding another conductor requires 15.0 cu. in. (FAIL).
This is why a 30 A device in a small box is tight: only 2 insulated conductors fit without a clamp, or 1 with one. The 3-conductor example above needs 17.5 cu. in. and cannot fit here. A volume calculation does not establish that the receptacle physically fits or is listed for the box.
Ampacity is separate from box fill
NEC Table 310.16 reference ampacities for 10 AWG, before applicable correction or adjustment factors; terminal temperature ratings and wiring-method rules also apply.
| Material | 60 °C | 75 °C | 90 °C |
|---|---|---|---|
| 10 AWG Copper | 30 A | 35 A | 40 A |
| 10 AWG Aluminum / copper-clad aluminum | 25 A | 30 A | 35 A |
NEC 240.4(D) caps overcurrent protection for 10 AWG copper at 30 A, subject to the exceptions specified there, which is why 10 AWG is paired with 30 A circuits. Ampacity does not change the box-fill count: the allowance depends on AWG size only, so copper and aluminum both count 2.50 cu. in. (40.97 cm³, converted) per conductor.
Reference: NFPA 70 (NEC) Tables 310.16 and 314.16(B), Section 240.4(D).
Frequently asked questions
How many 10 AWG wires fit in a 4" square box?
Depth matters: the 4" Square x 1-1/4" Deep (18.0 cu. in.) holds 7 counted conductors, while the 4" Square x 2-1/8" Deep (30.3 cu. in.) holds 12. These are conductor-only limits; subtract the allowances for devices, internal clamps, grounds, and other fittings.
How much space does a 10 AWG wire take in cubic inches and cm³?
2.50 cu. in. per counted conductor under NEC Table 314.16(B). Multiplying by 16.387064 gives 40.97 cm³; the code table rounds its metric entry to 41.0 cm³.
Does a 10 AWG ground wire count?
Yes: for the cable configurations shown here, all grounds together use 1 allowance based on the largest equipment grounding conductor (EGC), per NEC 314.16(B)(5). With 10 AWG as the largest EGC, that is 2.50 cu. in.; larger groups of grounds can require additional allowances under the applicable NEC edition.
Is 10 AWG volume different for aluminum than copper?
No: 10 AWG uses 2.50 cu. in. (40.97 cm³, converted) per counted conductor for either material. Ampacity differs, but the box-fill allowance depends on AWG size only.
Can a single-gang device box hold a 30 A receptacle with 10 AWG?
For the 3" x 2" x 2-1/2" Device Box (12.5 cu. in.), a device and ground allowance leave room for 2 insulated 10 AWG conductors without an internal clamp, or 1 with one. The 3-conductor receptacle example needs 17.5 cu. in. with its clamp and ground, so it does not fit this box; device dimensions and listing also matter.