There is a neat conversion App in the iTunes store for iPads and iPhones.
It is called the Kitchen Calculator Pro. There is a version that is not called pro, forgetabout it.
Anyway this neat App lets you convert volume to weight and the best thing is it asks you what ingredient you want to convert.
So if you select cups to grams you then get a list, in alphabetical order starting with Allspice, ground, bread crumbs, cornmeal, water, milk etc. For those of us who can never remember stuff like this it is great! I think it cost $2.99,maybe $3.99.