Data supporting a comparison of seed masses in crop species and their wild progenitors. The data files which fed into the analysis reported in the paper are: Grass_crops_raw.csv Legume_crops_raw.csv Veg crops combined.csv Beet_seeds_dissected.csv - mass of true seeds of beet; the data in the main 'Veg crops' file are for beet seed capsules, which are easier to collect and weigh. Cassava_EMBRAPA_*.csv - extra seed mass data from cassava, analysed separately from the main data, and described in supplementary material 2. Scripts used in processing the data (*.py) and a Makefile controlling some processing steps are included. There is also some extra data collected on other species of vegetable crops: Brassica spp., Chicory & Endive (Cichorium spp.), Leek (Allium ampeloprasum), and on fibre crops: Kenaf & Roselle (Hibiscus spp.), Jute (Corchorus olitorius), Hemp (Linum spp.). The data available for these was not sufficient to include them in our analysis, but they are provided here anyway.