The geospatial dataset maps organic carbon (OC) storage (kg OC m-2) and OC stocks (tonnes OC) of surficial soils across 438 Great British saltmarshes. The OC density for the surficial soils (top 10 cm) is mapped across 451.65 km2 of saltmarshes, identified from current saltmarsh maps of Great Britain’s three constituent countries; Scotland, England and Wales The spatial maps are built upon surficial (top 10 cm) soil bulk density and carbon data produced by the NERC C-Side project and Marine Scotland data combined with existing saltmarsh vegetation maps. The work was carried out under the NERC programme - Carbon Storage in Intertidal Environment (C-SIDE), NERC grant reference NE/R010846/1.