Characterizing the physical properties of single cells is of great interest for unraveling the heterogeneity in a cell population. Recent advances in micro-systems technologies and quantitative imaging have enabled measurements of the mass and growth of single cells. So far, three classes of techniques have been reported for such measurements. These are suspended micro-channel resonators (SMR) sensors, quantitative phase imaging (QPI), and pedestal resonant sensors. Here we compare the unique merits of each method and discuss their potential to evolve into multi-modal platforms for answering fundamental questions in biology and medicine.