Comparing the performance of pasture grasses often involves many small plots of about 10 m2. Dry matter yield is the standard measurement, but mechanical harvest may not be an option for small plots if grazing is also needed to provide a realistic environment. Hand harvesting within 0.25 x 1.0 m2 quadrats may not adequately cover spatial variability in yield, and requires a lot of drier space. An alternative may be to use a rising plate meter (RP) that non-destructively estimates yield across the whole plot before grazing. Once the RP has been calibrated against dry-matter harvests, three-hundred plots can be easily measured by a single person in a day. There are challenges with using a RP on tame grass plots: (1) different species of grass or density of stands may require unique calibration, (2) the sward density may change during growth changing the calibration, (3) there may not be a large enough variation in of growth across a plots to get an accurate calibration, and critically (4) if more drops of the plate are made during its use than its calibration, use may be more precise than calibration leading to RP yield differences that are not real. We wanted to test the hypothesis that calibration could be made over time, during the growth of Phleum pratense L., Festuca pratensis Huds., Phalaris arundinacea L., and Poa pratensis L. For growth in monoculture, each grass required a unique calibration curve. Calibration over time was possible when the sward grew from 5 to 15 cm, but the precision of calibration decreased as the grasses grew from 15 to 20 cm in height. Measuring plot yield by RP was more precise than hand harvesting in 0.25 x 1.0 m2 quadrats, but every experiment requires careful calibration of the RP for accurate results.