Input data used to model sediment grain size for the north-west European continental shelf. Data includes: Sediment groundtruth observations with measured fractions of mud, sand and gravel, also converted to two additive log-ratios. These total 45761 samples. Also included are the eight predictor variables that were used to model sediment grain size. These were: Bathymetry, Bathymetric position index at a 50-pixel radii, Bathymetric position index at a 434-pixel radii, Distance from coast, Current speed at the seabed, Wave peak orbital velocity at the seabed, and suspended inorganic particulate matter for summer and winter as two separate variables. Groundtruth observations were downloaded from a number of European government agencies and academic literature. A thorough filtering of samples was performed to delete samples collected prior to 1990 and samples where rounded sediment fractions were recorded (suggesting the values had been estimated and not quantitatively measured). Where sediment samples were located within the same pixel the mean of the sediment fractions was also calculated to produce an average value representative of that pixel. Predictor variables were downloaded from various sources. Bathymetry data and associated derivatives were downloaded from EMODnet bathymetry (http://www.emodnetbathymetry.eu/). Current speed and Orbital velocity of waves at the seafloor were modelled by Cefas staff. Suspended inorganic particulate matter layers were derived from data downloaded from Copernicus online portal (http://marine.copernicus.eu/).