This document specifies how to calculate: — the uncertainty of sound absorption coefficients and equivalent sound absorption areas measured according to ISO 354; — the uncertainty of the practical and weighted sound absorption coefficients determined according to ISO 11654; — the uncertainty of the object sound absorption coefficient according to ISO 20189; and — the uncertainty of the single number rating determined according to EN 1793‑1. Furthermore, the use of uncertainties in reporting measured or weighted sound absorption coefficients is explained.