A sensor for measuring a level of a liquid such as fuel and/or water in a tank such as a fuel tank. The sensor includes a stack of capacitors, each capacitor with one or more graphene measurement electrodes and one or more graphene reference electrodes. A measurement system is arranged to measure a capacitance of each capacitor between its measurement electrode(s) and its reference electrode(s) and thereby infer the liquid level. The graphene measurement and reference electrodes are formed in a single layer of graphene oxide by reductive etching.