One stick of margarine is equivalent to 1/2 cup. This measurement is standard across most brands of butter and margarine sold in sticks in the United States. A standard 1-pound package of margarine or butter contains four 1/2cup sticks. A 2-pound package contains eight sticks.
Shortening and margarine sold in tubs can be measured in cups with no changes to a recipe. One half-cup of shortening or margarine is equivalent to one stick of margarine. In some recipe substitutions, adding a small amount of water to shortening provides a result that is more consistent with the result of using butter or margarine.