A compilation of data from East and southern Africa is used to establish a relationship between precipitation and peak biomass aboveground in the herb layer (a crude measure of primary production). The regression equation is: peak biomass (kg ha^‐1) = 8.488 × precipitation (mm) ‐ 195.768, which predicts a peak biomass of approximately 800 kg ha^‐1 for every 100 mm of precipitation received above 20 mm. The usefulness and limitations of this result are discussed.