Manual cell counting is time consuming and requires a high degree of skill on behalf of the person performing the count. Here we use a technique that combines digital holography and phase contrast microscopy allowing label-free and completely non-invasive cell counting directly in cell culture vessels with adherent viable cells. Digital holography can provide both quantitative and qualitative phase information from a single hologram. The recently constructed microscope HolomonitorTM M2 combines digital holography with the benefits of the commonly used phase contrast microscope, allowing us to combine the advantages of light imaging with the possibility of achieving quantitative information on cellular shape, area, confluence and optical thickness. This project aimed at determining the accuracy and repeatability of cell counting measurements using digital holography compared to the conventional manual cell counting method using a haemocytometer. The collected data were also used to determine cell size and cellular optical thickness. The results show that digital holography can be used for non-invasive cell counting as precisely and much faster than conventional manual cell counting