A link to the lee powder dipper chart.

https://leeprecision.com/cgi-data/instruct/Dippers.pdf

The lee dippers use volume (38spl case ='s volume) to measure the weight of different powders. Hecse same dipper ='s 1.2gr/1.4gr/2.4gr etc.

You need to look at some reloading manuals and cross reference that data with the lee data. Slower powders use more powder per load than fast burning pwders. But that doesn't mean much, example:
reddot uses 4.1gr for a max load p+/125gr/38spl
pp uses 6.6gr for a max load p+/125gr/38spl

Both will take up the same case volume in the 38spl case.