Amplitudes in in vitro electrophysiological measurements refer to the value of currents or potentials recorded from one cell or a population of cells at a given time point. This chapter discusses amplitude measurements for in vitro slice electrophysiology and covers appropriate calculations for action potential amplitudes, field potential amplitudes, postsynaptic current/potential amplitudes, and steady-state current amplitudes. Like many electrophysiological measurements, technical considerations for precise calculations are important. These technical considerations are addressed at the end of this chapter.