SQL中不同测量单位之间的转换（在Access中）

I'm trying to program an access database but I'm using SQL for all my querying. I've got the database almost complete but I have one query that has me stumped. It is a database which contains recipes. I have a table in which I have all the conversions for cooking (Tablespoon to Teaspoon, Teaspoon to Cup, etc.). The user needs to be able to put in an ingredient using whatever units the recipe calls for (in other words, I cannot standardize the units, I have to find what they are). Then I need to be able to convert these into a standardized unit. This is where I'm having the problem because things like vegetables can come in cups, tablespoons, etc. whereas things like meats come in ounces, pounds, etc. I want to avoid creating a bunch of vb if/then's. I feel like there must be a way to do this with SQL but I can't seem to figure it out.I'm trying to program an access database but I'