ShapeCalc is an Excel-based tool that uses 2D crystal intersection widths and lengths to estimate 3D crystal shape. ShapeCalc provides 3D (S:I:L) shape estimates for 2D width-length (w-l) input data. Best estimates are found by comparing the sample w/l distribution with 2618 model w/l distributions covering shapes from 1:1:1 to 1:20:20. Model w/l distributions are obtained by 20000 random sections of a given model shape using the CSDCorrections algorithm (Higgins, 2000). For each model shape, the 20000 w/l datapoints are binned into 25 bins with w/l increments of 0.04. Binned distributions for all 2618 models are stored in the database tab. Compared to existing 2D-to-3D projection tools, ShapeCalc offers more robust constraints in 3D crystal shape (including uncertainty estimates) for a wider range of naturally occurring crystal shapes. ShapeCalc is described and published, with open access; Mangler, M.F., Humphreys, M.C.S., Wadsworth, F.B. et al. Variation of plagioclase shape with size in intermediate magmas: a window into incipient plagioclase crystallisation. Contributions to Mineralogy and Petrology 177, 64 (2022). https://doi.org/10.1007/s00410-022-01922-9