# Calculate electrical box volume needed

I am replacing some 15A 14/2 outlets. All went fine except the last. I think the box is not large enough.

• (3) 14/2 coming into the box; one is the live the other two go to other outlets
• All grounds in a wire nut, single ground going to outlet ground.
• 2 of the hot from the outgoing are connected via wire nut, single hot going into the push pin connector
• hot from the live in the other push pin
• the 3 neutrals are in the two push pins and the screw connector (no wire nut used)

How do I count this? I'm pretty sure the 3x2x2.5 box is not enough.

• This is a really good question and it got a really valuable answer. I'm bookmarking for my future reference. Thanks for asking it! Jul 22, 2020 at 1:17
• I still refer back to this answer a year later. The answer is great!
– Mike
May 16, 2021 at 15:54

All grounds count 1. (per @ThreePhaseEel's comment, more than 4 are now 1/4 count each as of NEC2020)

One yoke device (the outlet) is 2

6 wires terminating in the box are 6

If there are cable clamps in the box, those count as 1. If they are outside the box, they don't count.

14Ga so 2 cubic inches per count.

So: 18 or 20 cubic inches. Pigtails (wires that don't leave the box) are free. Wires count the same if they terminate on a wire nut or terminate on a device. Your box isn't big enough, you are correct about that. A box can be legit and still be hard to pack in (the free things are not really free that way) but the box you have is not legit as wired.

Side note. Using the backstabs is highly dubious and frowned upon by anyone who has removed a half-melted device using them, or actually had a fire started by them. How they ever got approval is beyond me. Use the side screw clamps or devices that have a screw clamp on a different type of back wire entry.

• Keep in mind that if there's more than 4 grounds, you need to add a quarter allowance for every ground in the box (this is brand new with the 2020 NEC btw) Jul 22, 2020 at 1:09
• I was gonna make the same comment about the backstabs. Glad you got there first. Also was going to make the same comment about the boxes. I've simply decided that I'm going to buy the biggest "x-gang" box I can find for whatever project it is I'm working on. It's just too difficult to stuff wires into something smaller. Jul 22, 2020 at 1:17
• My default minimum box is a 4x4x1-1/2 - or x2-1/8 - 4-11/16 square offers a good deal more room but the price differential is painful. I just got in a bunch of 5 gang "masonry" boxes which offer a decent amount of working room for busier locations at an attractive price, and screw into wood just fine. Jul 22, 2020 at 13:04
• If you use a square box for a single receptacle, what sort of cover plate do you use? Jul 22, 2020 at 16:24
• @JimStewart -- flat cover plates for square boxes in single gang apps are a thing, or you could use a single gang mud ring on the box for that matter. You could even use a two gang plate or mudring and then a cover with one side blank. Jul 22, 2020 at 23:54