The paper proposes the metrics for marketing communication in social media. The metrics are based on typical social media engagement measurements, but are calculated in relation to the concepts of content quality, valence and volume. The authors present a social media marketing communication experiment implemented in a real business environment of the e-shop Facebook fan page. The experiment results show that different effects were obtained depending on the content of posts (picture, video, album) related to the same products. In the case of video, the highest level of reach, while in the case of pictures, the highest level of engagement was achieved. The analysis of social media engagement metrics in relation to the published content type, dissemination process and time were proposed. The obtained results clearly show how complicated the analysis of social media communication could be and that the metrics have to be carefully designed to capture the relevant outcomes and aims.