A puck of high-permittivity, low-loss ceramic acts as a compact, very high-Q resonator — the frequency-setting element in dielectric-resonator oscillators (DROs) and cavity filters. Most energy is stored inside the puck, so its size and dielectric constant set the frequency. This tool uses the Cohn/Kajfez closed-form approximation for the dominant TE01δ mode. It's a ±2 % estimate for an isolated puck; shielding and a substrate shift it.