Kernel smut, Tilletia barclayana, is a rice disease that has been present in the Sacramento Valley of California since the mid 1980s. In recent years, the disease has become prominent in warm areas of the Valley. The objective of this research was to develop a method to evaluate the disease level in the field, and quantify losses due to kernel smut infection. In 2017 and 2018, affected rice fields of three common varieties were sampled at maturity. In each field, thirty, 1-square yard quadrant samples were hand harvested. From each sample, three sub-samples of ten tillers were randomly selected and inspected for kernel smut. Each quadrant sample was threshed, and number of smutted kernels, and grain, milling and head rice yield determined. To determine the number of smutted kernels in the grain, three 25 g rice sub-samples were soaked in a 0.27 M KOH solution for 24 hours to clear the hulls and make counting easier. The proportion of infected panicles predicted the number of smutted kernels per 25 g of grain. Number of smutted kernels did not affect grain yield. Milling yield was affected by number of smutted kernels in all varieties in both years, with percentage milling yield reduction rates ranging from 0.05 to 0.25. Head rice yield was only affected by number of smutted kernels in in 2018, with average reduction rates in percentage milling yield of 0.085. The results provide a method to evaluate kernel smut in the field and show that kernel smut can significantly affect the quality of rice.