Widespread use of microwave technology requires quantitative scale-up models. Currently, microwave models are typical qualitative in nature. This work focuses on rendering models quantitative and elucidating the scale-up behavior of microwave heating using numerical simulations. A commonly used bench-scale microwave reactor from the CEM Corp. (CEM Discover SP) is used for benchmarking. To enable quantitative modeling, microwave heating experiments are conducted and compared to COMSOL calculations to develop a calibration curve for the set point vs the actually delivered microwave power. Using the validated computational model, microwave-heating of various liquids in a wide range of vial sizes is investigated. The computational study shows that during the scale-up, the volumetric power absorbed passes through a maximum, whereas the energy efficiency and heating uniformity exhibit strongly nonlinear behavior. This work introduces a method for quantitative microwave models and insights into the scale-up of commercial microwave reactors.