Hi @Ruby_P -
We do not currently have a step-by-step process written up to do this, but have you seen this forum post that talks about creating AWC from SoilGrids data? I’m not sure if they’re using the same layers you are, but perhaps it will help to see some of the math written out.
I suspect that most of the steps can be done with Spatial Analyst Math functions like Times, or Raster Calculator, which is a favorite tool of mine for doing more complex raster math.
~ Stacie