When discussing gas pressure, you may come across the acronym WC or w.c., which is a measurement of pressure. WC stands for Water Column; it is a measurement based on an inch wide tube of water containing a hole at the side base of the tube. The taller the tube, the higher the pressure on the stream of water being delivered from the hole at the bottom.
For example, a 4" WC regulator refers to the pressure of the gas, not the width of the gas line. A typical 4" gas regulator can take the raw force of the typical 14" pressure of the unregulated gas line and reduce the pressure to the safe 4" WC, which is usable by an appliance. That said, most natural gas lines deliver gas to your home at a low 5-7.5" WC.