Monitoring cellular calcium concentration using fluorescent reporters can provide a rapid, proportional assay of G-protein-coupled receptor activation. Recording calcium changes in single cells, or cell populations, is relatively straightforward, but requires careful deliberation regarding the appropriate calcium reporter and experimental approach. Here, we describe strategies to ensure that calcium changes are recorded with good fidelity and minimal invasiveness. We highlight a range of issues that need to be considered within the design of an experiment to measure cellular calcium, and suggest strategies to avoid common pit-falls.