This standard specifies requirements and describes procedures for the measurement of ambient noise in a room. The measurements may be made at a specified point in the room, in a defined region of the room, or the measurements may be made to represent the space-average sound pressure level throughout the room. Two methods are offered: a survey method for quick evaluation and an engineering method for a more precise assessment of the ambient noise level. Both fixed and moving measurement microphones are allowed. The scope of this standard includes all types of ambient noise including building utility systems and exterior noise intrusion from street traffic and aircraft. Noise sources excluded from the scope of this standard include noise from building occupants and transient noise sources. The results of the measurements obtained via this standard are intended to be used to compare measured sound pressure levels with acoustic criteria similar to those presented in ANSI/ASA S12.2. It should be noted that by its very nature, ambient noise is not always stationary in time. Consequently, one should not expect to obtain identical results when a procedure specified in this standard is used in the same room at a different time.