At a very minimum, any undergraduate student majoring in Economics should take single and multivariate calculus, linear algebra, and a good course in probability and statistics. From there on, how much more math to take will depend on exactly what you want to do after you graduate.
You will see this theme repeated as you search the web for answers to this question. Here is the list, according to Greg Mankiw, from Harvard University. And here’s the list, according to Tom Sargent, from NYU. Sargent’s list is very good in that it goes into a lot of detail about what undergraduate and graduate students in Economics ought to know about mathematics and statistics at different stages in their careers.
One day I’ll prepare a similar list to that of Sargent’s based on Cal Poly’s course catalog.
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