I am installing numerous two gang receptacle boxes in a shop/barn area.
The boxes are regular metal 4 square outlet boxes connected to 1/2" EMT conduit. There will be six #12awg wires coming in to each box and two duplex receptacles in each box. I will be putting wire nuts on the pigtails, so there will three red wire nuts also. I am not sure of the formula for how many wires and devices you can put in a regular 4x4 box. Does it have to be a deeper bigger box for this many wires and devices, or am I okay.
Thank you, Guy

The #12 wire each need 2.25 cubic inch, each device counts as two wires, so there is a total of 22.5 CI needed. I am assuming there is no ground wire. If there is a ground wire all will equal one wire.

The box needs to be no smaller than a 4"x4"x 2-1/8" deep box, not considering the cover. If this box is surface mounted using what is called a raised cover to hold the devices, it also has volume of space which is stamped on the inside, and can be added to the outlet box space.

In addition, if wire goes in and out of box, it counts as 1 wire, if you cut the wire, it now counts as 2 wires.
Don't skimp on box size. You may need to add more later. Dimmers and GFI's are large devices. Stranded wire can be less stressfull(physically) on devices, than solid.