The data set summarizes the input and output data for the study Large stocks of permafrost soil organic carbon and nitrogen in Arctic river deltas (Fuchs et al. in prep.). The data set includes information for 211 Arctic river deltas including the size, water area, permafrost distribution, deposit thickness, volume of alluvium, soil carbon and soil nitrogen stocks; and was compiled in an analysis based on archived and newly acquired data. In addition, the soil carbon and nitrogen stocks for Arga Island in the Lena Delta and Yedoma deposits in Arctic deltas are included in the data set.The area for each delta (in km2) is based on the geospatial layer (doi:10.1594/PANGAEA.968908), that was created by digitizing the spatial extent of each delta based on available Google Earth images. The area (km2) of the resulting polygon shapefile was calculated using ArcMap 10.6. This simple mapping provided a first-order estimation of the total area covered by Arctic deltas. In our approach, we used a definition of 'Arctic delta' that includes typical prograding deltas but also estuaries and alluvial fans ending in the Arctic Ocean as well as inland deltas. This includes deltas of size >10 km2 and a representative subset of micro deltas (< 10 km2). We set the beginning of a delta as the point where the river channels start to spread and lead independently to the sea and develop a distinct fan. Digitized Arctic deltas therefore include not only deltaic, fluvial deposits in a strict sedimentological definition, but are based on a geographic definition of deltas.The percentage of water bodies for each delta were calculated based on a global surface water layer (Pekel et al. 2016) and include areas, which are covered by water for more than 95% of the time of the ice-free season. The permafrost distribution (in % of area) within each delta was calculated based on the most recent permafrost map (Obu et al. 2019) by intersecting the permafrost distribution layer with the mapped delta land areas.For the estimation of the thickness (m) of delta deposits, we used a correlation between the size of the delta and the deposit thickness that was available from five Arctic deltas. Based on this (linear) correlation we estimated the thickness for all the remaining deltas. This is based on the assumption that larger deltas have a higher sediment load and therefore also a greater thickness of deposits. For the sediment volume (km3), we not only multiplied the area with the deposit thickness but included the information about water area, active layer depth, ice-wedge volume, and permafrost distribution in order to estimate the amount of frozen and non-frozen sediment volume for each delta. For further information on the deposit thickness estimation, please see Fuchs et al. (in prep.)In combination with the synthesis data set (doi:10.1594/PANGAEA.968906), all the above-mentioned parameters served as input for estimating the total carbon and total nitrogen stocks (Pg) for each of the deltas. Hereby we ran a depth decay model for carbon and nitrogen input data in order to avoid overestimation of carbon and nitrogen in deep deposits. In addition, we calculated the soil organic carbon and nitrogen stocks for 1-m depth increments for each delta and in a final step summed these values to every delta's depth to derive the total soil organic carbon and total nitrogen for each Arctic delta. In order to account for the variability in the input parameters, an R-based model was developed that randomly samples a value (for each input parameter) that is within the lower and upper uncertainty range. The model is run 10,000 times and calculates carbon and nitrogen stocks for 1-m depth increments for each delta during every iteration. Also, the depth of deposits varies in each iteration depending on the 95% confidence interval depth range of every delta. In the end of each model run, the carbon and nitrogen stocks are summed for each delta to the specific depth resulting in 10,000 estimates for carbon and nitrogen stocks. This allows in a final step to calculate the mean carbon stock including the 95% confidence interval for each Arctic delta. For more details on the upscaling of carbon and nitrogen stocks in Arctic deltas, see Fuchs et al. (in prep.).