A medium donut measuring almost 4 inches across contains 255 calories. While eating one donut with coffee for breakfast won't ruin your diet plan for the day, consuming two or three of them will. The calories in donuts are primarily empty calories, as donuts are low in nutrients.owever, that can be hard to do, and donuts are ubiquitous at meetings, socials and other gatherings. The important thing about the calories in a donut is the nutrients that they do -- or don't -- provide.