We describe several methods for calibrating different neutron moisture meters. The simplest was found to be that of calibrating one “master” probe and comparing other probes with this under similar field conditions over a range of soil water contents. If several probes are available initially, plastic absorbers of various thicknesses can be used as secondary standards to establish a regression equation for the different probe. From the slope and intercept values obtained, a reference regression equation can be developed that can be used to calibrate other probes in the laboratory.