I am just getting started with a bread machine, and like to convert recipes to metric weight from cups and tespoons, etc. I have found convert-me very useful to make my own conversion tables in a spreadsheet.
The final column in my table for each food is density, calculated from one of your volumes in ml and weight in grams. From this I can convert individual recipes from cook books easily.
However, it would all be much easier if you would just show a table of foods with their densities. Then it would be easier to convert any volume, be it a bushel or a peck, into a weight.
It could even just be shown in your list of foods below the calculator - Water (1), Strawberries (0.64), Oil, Olive (0.91). Then there would be no need for your user to enter anything into boxes.