I've got 8 rasters all of different sizes. What is the proper syntax, for the raster calculators of either Arcmap or Qgis, that will output a raster that covers the extent of all my data not just the area of overlap?
No data values in a raster in ArcMap will nullify any summation resulting in nodata for any cells beyond the extents of the total area. Your workaround would be to produce rasters with the maximal extent, set the nodata values to zero and then sum. Not a pretty prospect and not necessarily what you want.