The number of total carbohydrates in a product includes both sugar and fiber. If you are trying to reduce your sugar intake in general, knowing what proportion of your carbohydrate intake is sugar allows you to track how you're doing and adjust your eating habits, if necessary. The nutrition label on a product contains the numbers you need to perform some simple math to get your answer.
Read the nutrition label and find the lines for the total carbohydrates and sugars. The total carbohydrates will have both a percentage and a number in grams. Use the number in grams for this. For example, a label lists 28 grams total carbohydrates and underneath it on the line marked "Sugars," it lists 6 grams of sugar.
Divide the number of grams of sugars by the number of grams from the total carbohydrates line. For this sample label, you would divide six by 28 to get 0.214.
Move the decimal point two spaces to the right or multiply by 100, if you prefer using an equation, to get you the percent form of the number. Using the 0.214 from Step 2, 21.4 percent of the total carbohydrates are sugar.
Remember that all sugars are counted in the sugar line on the label, not just added sugar.