I would like to be able to add volume of liquids as this is the most common measure. The conversion to weight could be calculated by the program.
You can edit a copy of the foods you want and add the volumetric measures you use as serving sizes. I have the opposite problem - a few foods only have volumetric units. For these foods, I typically approximate 1g ~ 1ml. Cronometer doesn't have a reliable source of data for mapping liquid foods to their density, so they can't add the information for you.
Thanks robartsd, for the reply. It is not so much serving sizes but adding ingredients by volume instead of weight. Rarely are ML available, occasionally FL OZ (requires another conversion over here in Aus) and sometimes other tsp, tbsp etc. I would like ML as a default, like g for weight. And yes, thids would naturally need the mapping to be done by the database (a thing for which computers are excellent).