A twenty four hour, single number, equivalent noise level usually calculated from measured hourly equivalent noise levels where certain corrections have been added to the evening and night time noise intervals to represent a penalty factor. The evening period defined from 1900 to 2200 has a penalty of 5 dB added to the measured levels while the night time period of 2200 to 0700 has a 10 dB penalty added. Thus a higher overall level is obtained for the complete 24 hours compared to the actual measured hourly levels obtained by normal logarithmic addition of the 24 separate Leqs.

Other shorter periods can be combined to produce the overall CNEL as long as the appropriate corrections are applied depending on the time of day that they were collected, for example 15 minute or 5 minute periods that will provide more detail when inspected at a later time.