box size for rf

You don't provide enough information for anyone to give an intelligent answer.

Do you mean how far away should the box be from the circuit board? Are you concerned about EMI from the device, or are you concerned about shielding the circuit from external noise, or both?

What frequencies are you working with? What signal levels are you working with? etc, etc, ...

There isn't one rule that fits all situations.

The box should have the smallest dimensions possible in all three directions. This pushes box resonances above the useful gain frequency of the transistors and reduces coupling between parts of the circuit.

it is depand on your freq. typ. less then 0.5 LAMDA in the air at your freq.

but u can use also a "popovitch" it will help u

the problem with popovitch is that : it is workink in genaral projeck only in "kllal atzba" no in furmula !