WASHINGTON — Diners will soon know how many calories are in that bacon cheeseburger at a chain restaurant, the pasta salad in the supermarket salad bar and even that buttery tub of popcorn at the movie theater.

The Food and Drug Administration announced long-delayed calorie labeling rules Tuesday, requiring establishments that sell prepared foods and have 20 or more locations to post the calorie content of food and beverages “clearly and conspicuously” on their menus, menu boards and displays. Companies have until a year from now to comply.

“Americans eat and drink about one-third of their calories away from home, and people today expect clear information about the products they consume,” FDA Commissioner Margaret Hamburg said.