Which Lens do i need

Hi

What lens is best for round the house 2.8mm 6mm or 4mm i have five cameras the distance from the cameras to where i need to see is between 20 to 30 foot

Try a lens calculator http://www.theiatech.com/calculator/

I did look at that but i dont under stand it im useing 2.8mm lens but i have a feeling they are to much for just round the house

2.8mm is has a wide field of view, good for overall viewing of what's going on, but not too much detail. As the mm get higher the area is smaller/closer but with more detail.

i would say the 4mm is a better option