This standard specifies methods for measuring the sound pressure levels on a measurement surface enveloping a noise source (machinery or equipment) in a free-field test room or a hemi-free-field test room. The sound power level (or, in the case of impulsive or transient noise emission, the sound energy level) produced by the noise source, in frequency bands of width one-third octave or with frequency weighting A applied, is calculated using those measurements. The resulting sound power levels and sound energy levels include corrections to allow for any differences that might exist between the meteorological conditions under which the tests are conducted and reference meteorological conditions. In general, the frequency range of interest includes the one-third-octave bands with mid-band frequencies from 100 Hz to 10000 Hz. In practice, the range is extended or restricted to frequencies beyond or within these limits, to those between which the test room is qualified for the purposes of the measurements. The methods specified in this Standard are suitable for all types of noise (steady, non-steady, fluctuating, etc.) defined in ISO 12001. The noise source under test may be a device, machine, component or sub-assembly. The maximum size of the noise source depends on requirements regarding the radius of the hypothetical sphere or hemisphere used as the enveloping measurement surface. The test rooms that are applicable for measurements made in accordance with this Standard are an anechoic test room or hemi-anechoic test room, also called, respectively, free-field test room or a hemi-free-field test room. Information is given on the uncertainty of the sound power levels and sound energy levels determined in accordance with this Standard, for measurements made in limited bands of frequency and with frequency weighting A applied. The uncertainty conforms with that of the precision grade of accuracy (grade 1) defined in ISO 12001.