AbstractA simple instrument for estimating the yield of herbage from measurements of height has been tested in cutting and grazing experiments. The instrument consists of a verticle graduated shaft and two linked aluminium discs which settle on the herbage. The height of the discs from the ground is recorded. Highly significant relationships were established between the yield and the height of herbage. Linear regressions explained 80–90% of the variation in the cutting experiments, and 39–62%in the grazing experiments. The errors attached to the estimated yields were high, but, because of the simple construction, low cost and rapid operation of the instrument, it is concluded that it has many useful functions in grassland research and managem