To find out how much naturally occurring sugar is found in an apple, consult the nutrition information on NutritionData.Self.com, AuthorityNutrition.com or FatSecret.com. The exact amount of sugar in an apple varies by apple variety and size.
According to Fat Secret and Authority Nutrition, raw Gala apples with the skin have around 10.4 grams of sugar per 100 grams. A medium apple of the same variety, with roughly a 2 3/4-inch diameter, may contain between 14 and 18 grams of sugar. Given this information, it is possible to measure an apple or weigh it on a kitchen scale to accurately estimate the amount of sugar it contains.
Fuji apples are slightly higher in sugar than Gala apples, with roughly 11.7 grams of sugar per 100 grams, according to Authority Nutrition. Granny Smith apples are lower in sugar, with only 9.6 grams per 100 grams. The chart on this website also allows users to input their own amounts, making it possible to weigh your apple and find out exactly how much sugar it contains.
Self Nutrition Data notes that a large portion of the calories in apples are derived from sugar. Apples are 95 percent carbohydrates by composition; however, they are rated as a three on the glycemic index, meaning they do not cause a notable spike in blood sugar.