One of the large industrial needs is the use of sound level meter (SLM) especially in noise monitoring even occupational and/or environmental, the calibration of this sound measuring device is essential during the last decades. The coupler approach is regarded as the most practical to apply of the SLM calibrating techniques required by the standard IEC 61672. In this method some tests have to be accomplished to judge the measurement results. The calibration performed within frequency range of 31.5Hz to 8kHz. The results showed that the calculated uncertainity lies within the order of magnitude between 0.3 - 0.45dB. The purpose of this work to assess and analyses the factors that affect the coupler method of SLM calibration method with their associated uncertainties in accordance with the Guide to the expressions of Uncertainty in Measurement (GUM). Additionally, a case study covered in details for the calibration of this equipment.