Understanding the primary productivity of salt marshes requires accurate estimates of biomass. Unfortunately, these estimates vary enough within and among salt marshes to require large numbers of replicates if the averages are to be statistically meaningful. Large numbers of replicates are rarely taken, however, because they involve too much labor. Here, we present data on a fast, non-destructive method for measuring aboveground biomass of Spartina alterniflora and Phragmites australis that uses only the average height of the five tallest shoots and the total density of shoots over 10 cm tall. Collecting the data takes only a few minutes per replicate, and calculated values for biomass compare favorably with destructive measurements on harvested samples.