Ever thought of google?
I got this:
There is no recommended daily allowance (RDA) for sugar. In fact, some experts believe we need no sugar at all. On the other hand, weight loss surveys have shown that diets containing very small amounts of sugar are less easy to stick to.
Official US Guidelines advise a maximum of 40g refined sugar for every 2000 calories consumed. This equates to 8 percent of calories.
Note: Refined sugar is not only table sugar - it includes the sugars in a wide range of processed foods (e.g. breakfast cereal). So remember to read food labels and choose lower-sugar brands.