This dataset is a cross-country convenience sample of primary data measuring crop production and/or area by farm size for 55 countries that underlies the article entitled "How much of the world׳s food do smallholders produce?" (DOI: https://doi.org/10.1016/j.gfs.2018.05.002). The harmonized dataset is nationally representative with subnational resolution, sourced from agricultural censuses and household surveys. The dataset covers 154 crop species and 11 farm size classes, and is ontologically interoperable with other global agricultural datasets, such as the Food and Agricultural Organization׳s statistical database (FAOSTAT), and the World Census of Agriculture (WCA). The dataset includes estimates of the quantity of food, feed, processed agricultural commodities, seed, waste (post-harvest loss), or other uses; and potential human nutrition (i.e., kilocalories, fats, and proteins) generated by each farm size class. We explain the details of the dataset, the inclusion criteria used to assess each data source, the data harmonization procedures, and the spatial coverage. We detail assumptions underlying the construction of this dataset, including the use of aggregate field size as a proxy for farm size in some cases, and crop species omission biases resulting from converting local species names to harmonized names. We also provide bias estimates for commonly used methods for estimating food production by farm size: use of constant yields across farm size classes when crop production is not available, and relying on nationally representative household sample surveys that omitted non-family farms. Together this dataset represents the most complete empirically grounded estimate of how much food and nutrition smallholder farmers produce from crops.