Translating Vitamin % into mg/mcg

I'm trying to use the Health Tracker in OH, but am running into difficulty creating custom foods. Why does OH insist on asking for mg or mcg when one has to add vitamin contents of foods as opposed to using percentages. Most food labels use % for vitamins. How do I translate % into mg or mcg?????

They are percentages of Recommended Daily Intake, so use the chart here to get that #

http://en.wikipedia.org/wiki/Reference_Daily_Intake

and do little math.