Lightroom :: Raw To JPEG File Size Rule Of Thumb

I’m wondering if there is a rule-of-thumb that one can use to predict the approximate size when exporting a raw file in Lr to a jpeg file.  For instance, would an average 25 Mb raw file convert to about 5 Mb jpeg with the Lr export quality set to 100?  To about 3.5 Mb with a quality of 80? …
 
I know the size will vary, but when I am exporting a collection of raw files and I have set the max file size to a certain amount, Lr sometimes won’t convert all the images because I have limited the file size too small.  I’d like to be able to get a handle on some sort of quality/file size relationship before I start the export process.