Most trenches require a minimum depth or 18 ” on top of the pipe or cable. This claculater is set to 24 inches which allows most sizes of pipe to meet minimum residential codes.When digging a trench going deeper is often better to avoid future damage. For example some electrical lines must be 40″ to allow a margine of safety.

PRO TIP:
Dont forget the tracer wire or burial tape to identify your buried lines.