The accuracy of different models for simulating the area of mature leaves on the main stem (PLA) of maize using thermal time was investigated. The accuracy of sub-models for simulating the area of individual mature leaves (LAn) and the number of mature leaves (Xn) was also determined. Measured data from six fully irrigated crops (three cultivars planted on two dates), as well as from independent data extracted from the literature, were statistically compared with simulated values. PLA was best simulated using an exponential function for the Xn submodel together with a bell-shaped function for the LAn sub-model. The average simulation error of the most reliable complete PLA model was 16%.