I believe that the most common electrical box for a wall-mounted fixture is a 4" octagon box such as this 4 in. Drawn Octagon Electrical Box with NMSC Clamps and Bracket. However, if you know which fixture you will install, I would look at its installation instructions. I bought a very narrow sconce that required a 4" x 2" box (typically used for a single wall switch) for installation without the adapter for the wider octagon box.

When you attach the box to the stud, it will be very strong.

-- amateur

Electrical safety tip: Instead of going straight across an open stud bay, that cable should be run close to the stud, up the wall, over, and then down to the point where it goes through the stud.

In my house, the cable is attached to the studs with clips (example). As Sammy wrote, the cable doesn't just flop around inside the wall.

My electrician wants to leave it like it is and wants me to drywall over it. Then he will attach a box to the drywall.

Don't do this. As you've been told in previous threads, your electrician is horrible. Everything should be done before putting up the drywall. Have the 'electrician' mount the box before putting up drywall. Have him staple the cable properly to the studs. Don't let him bury junction boxes behind drywall. The list goes on and on.

If the cable needs to be in a different stud bay then it HAS to be in that stud bay before putting up drywall. There is ABSOLUTELY no arguing that.

Thanks to all.

I don't know why I thought the box would be blue. Maybe the blue boxes are for after construction?

I think I can move the white clip to the other side where the metal pipe is, run the wire against the studs. and nail the clip back in. I didn't know what the white clips were called. I told him the light needed to be centered, and the vanity was there so I am not sure why the wire was put closer to the corner.

Every time I don't like what he has done, I have to pay him to redo it. He charges by the hour, so it doesn't matter to him if he has to redo work. Well, at least it gets fixed, but it sure is costing me a lot to redo. In the other bathroom, the wiring is run across 4 different studs. I know the wire is not long enough to clip it to the side of the stud so maybe I can put blocking in there and clip it to that. Tile is going on that wall so hopefully that is more protective than just drywall.

Greg_2015, ok thanks. I did not understand how it could go from one area to another after drywall was up. He really is an electrician. I checked his license. I think the mentality around here is that homeowners want to save money so contractors do what they can to help them save money, but I have told him multiple times that I want it to code no matter what it costs. We are in a very poor area. Everyone wants the lowest cost and they don't care about codes, I guess. My old by-the-book electrician would have never done this kind of work. He said expectations of some homeowners wanting to do things "cheaper" is one of the other reasons he moved. He was too high priced compared to others and had trouble getting jobs with homeowners complaining about his charges. Now that man has some ethics!

I will put the boxes in myself once I buy the lights and move the clips. I had the electrician come back to fix the blank boxes in the wall at my cost. Good electricians are worth their weight in gold!

Cables should be secured with a staple (or clip) about every 4 feet minimum (I'm not sure the exact distance) but use another staple anywhere that you'd feel it needs to be to keep the cable from flopping around and make it neat and tidy.

And it needs to be secured within 12" of where it enters a box.

I have to disagree with Sammy that the wire should go up and over and down to reach the location. Cable is frequently run across stud bays. It's only a 1.5 to 2 feet. That's fine. There is no safety concern about that. If it's attached securely with a staple at each stud (or supported by running through a hole in the stud) then it isn't an issue.

You say that you want the fixture "centered". Centered with respect to what? Would that be a problem regarding where to put the light? Can you take another photo (from farther away) and indicate where you want the fixture?

Mark on the wall where you want the box to be placed. If it is at the stud, the box can be attached to it, and you'll need one that allows for that. If it is not near enough to the stud, you'll need to put a board behind it and attache the box to the board.

Many square boxes are for switches, not lights. You have to look at the screw hole layout to tell the difference.

Thanks. I bought the wire clips today so I will get them installed.

The center of the vanity will put the light between the stud and the metal pole. It will be 7" off center if I put it on the right of the pole, and 3" off center on the left of the stud. So, the light will go on the left side. That is as good as it will get.

I believe the light said it needed a 4" hexagon box. Hopefully, someone at Lowe's can help.

Thanks, everyone.

Generally for ceiling use, there are round, shallow electrical boxes that can be attached to the front of a stud and then wired up. The drywall is then carefully cut around the box when it's installed. I used one of these because the stud centered between two windows was where I wanted to install a sconce.

Thanks, wdcruise.