Electromagnetic resonators are often used to detect foreign materials. Here we present a simple experiment for the measurement of liquid level. The resonator, consisting of a coil and a capacitor, is brought to resonance by an external magnetic field source, and the corresponding resonance frequency is determined using Fourier analysis combined with nonlinear curve-fitting. A medium inside the resonator alters its resonance frequency, depending on the liquid level of the medium. (Contains 3 figures.)