Office environments involve various kinds of furniture ensembles which are expected to reduce noise: open and enclosed workstations, pods, sofa groups, chairs, and booths. The diversity and market is strongly growing. However, there is no standardized method to declare their sound reduction properties. Our purpose was to introduce a laboratory method to determine the sound reduction of furniture ensembles. An easy-to-understand single-number quantity was desirable to facilitate communicaton with end users and designers who usually do not have education in acoustics. The test is conducted in a reverberation room. Speech source is placed to the position of the occupant's mouth inside the ensemble. Sound power level (ISO 3741) is determined with and without the ensemble. The level difference in 1/1-octaves describes the sound reduction. The single-number outcome of the test is the speech reduction index D_S, which describes how much the ensemble reduces the A-weighted sound level of normal effort speech outside the ensemble. Six furniture ensembles were tested to demonstrate the method. The results show a consistent pattern. The measurement uncertainty is less than 1 dB. The paper is based on Hongisto et al. (2015, Acta Acust united Ac).