This paper analyzes the shape of rain area size distributions (RASDs) observed by radar in tropical and midlatitude regions. The rain area is defined, with respect to a rain threshold τ, as the area, inside a contour, where the rain rate is higher than τ. The size considered is the diameter of the equivalent circular area D. The reflectivity peaks inside the rain areas are numbered and the rain areas put together by classes having the same peak number. The size distributions of the rain areas containing the same number of peaks p are well fitted by lognormal functions, the parameters of which, ¿p and σp, are weakly dependent on the conditions of the peak determination. The parameters ¿p and σp are found to be linked by a power relation. For D < 6 km most of the rain areas are single peaked. The RASD without peak number distinction is a lognormal mixture. Using the relations obtained for ¿p, σp, and the rain area number as functions of p enables one to simulate RASDs with results in good agreement with the observations. Because of the limitation in the radar sampling at both ends of the RASD and the decrease of area number with increasing size, the radar-observed RASDs are severely truncated. The possibility of an approximate fitting of the truncated RASD with diverse functions is discussed. At the intermediary values of the threshold, i.e., for τ ranging between 3 and 12 mm h-1, where the RASD is easiest to compute, the slope of these truncated distributions is not strongly dependent on the threshold. This slope appears not to be very sensitive to the minimum and maximum distances bounding the domain where the rain field is observed. The RASD is found to be sloping more over sea than over land. The slope of the RASDs shows a small diurnal variation but no significant annual variation. The perimeter to area (fractal) dimension of the rain area for the sample without peak number distinction is around 1.35. Single-peaked and multipeaked rain areas have different perimeter to area dimensions, ~1.23 and 1.38, respectively. These values are almost independent from the threshold and from the location of the domain observed.