Properties of TE011cylindrical, microwave cavities containing cylindrical samples of various radii and dielectric constants are calculated. The properties considered are the resonant frequency, quality factor (Q), relevant magnetic filling factor for spin transitions (&eegr;), and a signal sensitivity factor (Q&eegr;) for a lossless sample. Sample sizes range from zero radius to full cavity radius with some experimental data on less than full length samples. The choice of dielectric constants ranges from one to sixteen. The data are presented in dimensionless form since they will be of use to other ESR experimentalists. It is shown that use of large samples is undesirable even if they are lossless. Furthermore, elongated cavities (D/Lratios less than one) are to be preferred over shortened cavities.