How many calories are in a medium popcorn with butter?

It depends on whether the popcorn is homemade or a ready-made brand bought from a store or movie house, etc. It also depends on how many ounces or grams are in your medium size portion. Medium size portions are not always the same size. Please feel free to ask the question again and include more detail. Meanwhile for the calories in popcorn by the ounce or 28g, both buttered and plain, see the page link, further down this page, listed under Related Questions.