What's the minimum depth I'll need for my electrical box build?

[Theredsasquatch]

Box will have ssr's and pid's also planning on doing a small computer style fan, looking to buy a box but I'm not sure what dimensions are minimum to fit the largest components.

 

[BeardedBrews]

https://photos.app.goo.gl/C7XSvRyDQks8ZZvN7

5 inches of inside depth feels pretty good, but you do still have to make sure the PID doesn't hit the contactor.

https://www.amazon.com/dp/B005UPANU2/ref=cm_sw_r_cp_api_i_fQY9Cb8T21JXX

 

[doug293cz]

When in doubt, you can build block models of your components out of cardboard or construction paper, and place them where you plan to in your panel, to check for interference.

Brew on

 

[processhead]

When planning, consider a couple things: 1) What gets mounted on the inner back-panel. 2) What gets mounted in the door/cover.

Typically, you will want a panel deep enough to so that the deepest door-mounted device(s) will clear the shallowest stuff that gets mounted on the inner panel, (typically, terminal blocks and wire harness).

Like doug293cz says, models and mock-ups can be useful planning tools before you start buying hardware.
Device datasheets usually have physical dimensions for products, so check those out.