A model for estimating reverberation time and sound pressure level in rooms with absorbent ceiling treatment is presented. The model presumes that the sound field is represented by a grazing and non-grazing part where the term grazing refers to sound waves propagating almost parallel to the ceiling.  It is shown that the sound pressure level and reverberation time are approximately determined by the non-grazing and grazing part, respectively. The effect of scattering objects, such as furniture’s, is quantified by estimating the energy transfer from the grazing to the non-grazing part. For this purpose, a measure denoted equivalent scattering absorption area is introduced. This parameter is well adapted for the reverberation formula presented. Calculated parameters according to the theory are compared with measurements. It is shown that reverberation time and sound pressure level are acting quite independently and not according to the classical diffuse field theory. It is recommended to consider both parameters in room acoustical design.