Box fill calculator

Count what's going in the box. Every item gets its own line, so you can see exactly where the room goes.

The box

Box

Box volume

in³

Plus ring, extension or cover

in³

Wires

Size	Spliced or ending Spliced or ending Each insulated wire that enters the box and is spliced, terminated or ends there counts once. Count neutrals and travelers, but not grounds. 314.16(B)(1)	Passing through Passing through A wire that runs through the box without a splice counts once. If it's looped or coiled 12 in. or longer, use the next column. 314.16(B)(1)	Loops ≥ 12 in. Loops 12 in. or longer An unbroken loop or coil at least 12 inches long counts twice. 314.16(B)(1)
18 AWG 1.5 in³ each
16 AWG 1.75 in³ each
14 AWG 2 in³ each
12 AWG 2.25 in³ each
10 AWG 2.5 in³ each
8 AWG 3 in³ each
6 AWG 5 in³ each

Show 18 and 16 AWG

Don't count grounds here, or fixture wires and pigtails that start and end inside the box.

Devices, clamps and grounds

Devices (yokes)

Largest wire on the devices

Fixture studs or hickeys

Largest ground wire

Isolated-ground wire

Internal cable clamps

How this is calculated

Volume allowances per conductor come from Table 314.16(B)(1). Standard metal box volumes come from Table 314.16(A).
Each conductor that starts outside the box and ends or is spliced inside counts once. A conductor that passes through unbroken counts once, or twice if it's looped 12 in. or longer.
One or more internal clamps count once, based on the largest conductor. Each support fitting counts once.
Each device yoke counts twice, based on the largest conductor connected to it.
All equipment grounding conductors together count once, based on the largest. Isolated-ground conductors per 250.146(D) add one more.