The United States (according to the American material testing standards ASTWE-90, E-413) adopts the sound insulation grade, that is, the STC (Sound Transmission Class) grade. STC is a simple numerical grade. In most cases it is equal to Rw. Can be used interchangeably.

STC is measured for a single component under laboratory conditions. The actual on-site sound insulation performance uses the noise isolation level NIC to be more accurate. NIC measures the total amount of attenuation of sound from one room to another, regardless of the path the sound travels.

The experimental procedures of the STC and NIC systems are the same, and the methods are equivalent. They are both used to evaluate the ability of sound insulation components to block people's speech sounds. They are imprecise ways to evaluate and measure isolation between rooms and bedrooms where machine noise is present, isolation from aircraft noise, and isolation from sources of non-verbal noise that may be bothersome. However, for airborne sound noise in multi-family houses, STC and NIC provide good guidance for comparing different components.

For example, after testing, a laminated insulating glass (specification: 3mm glass +0.76PVB film+3mm glass+12mm air layer+6mm glass) the STC is 39, when doubling the air layer thickness to 25mm the STC is 42.