A jelly or jam doughnut contains 96 calories per ounce, according to the U.S. Department of Agriculture's National Nutrient Database for Standard Reference. The number of calories in any given doughnut depends on the size and weight of the doughnut.
The USDA calculates an average jelly or jam doughnut measuring 3.5 by 2.5 inches as having 289 calories. A jelly doughnut from Dunkin Donuts comes very close to that calorie count at 270 calories, 126 of which come from fat, according to About.com. A jelly doughnut from Krispy Kreme is also right at the USDA estimate with 290 calories, according to My Fitness Pal.