How this calculator works
Popcorn is a whole grain that turns steam inside the kernel into a sudden expansion, so a small volume of kernels becomes a large volume of popped corn. A tablespoon of kernels makes about three cups, which is why the kernel amount is so much smaller than the bowl. The popping method decides the calories: air popped corn is only the grain, oil popping adds fat, and microwave and theatre styles carry more fat and flavourings. The salt figure is a light seasoning of about 0.2 g per cup; cinema style popcorn can carry several times that. Portion sizes follow common cinema cup sizes, from a small three cup portion to a large ten cup bucket.
Formula
cups = people x cups per person. kernels (tbsp) = cups / 3. oil (tbsp) = kernels x 0.5 when popping in oil. salt (g) = cups x 0.2. calories = cups x kcal per cup, where the figures are 31 for air popped, 45 for oil popped, 50 for microwave butter, 55 for microwave cheddar, 60 for theatre butter and 120 for caramel corn.
Worked example
For 6 people at a large 10 cup portion the total is 60 cups. Kernels are 60 / 3 = 20 tbsp, which is 1.25 cups of kernels. Oil popped, that needs 20 x 0.5 = 10 tbsp of oil. At 45 kcal per cup the popcorn is 60 x 45 = 2700 kcal, or 450 kcal per person. The same amount of theatre butter popcorn is 60 x 60 = 3600 kcal.
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Frequently asked questions
How much popcorn is one serving?
About three cups is a normal single portion, and a large cinema bucket is closer to ten. Popcorn is bulky but light: three cups of air popped corn is only about 24 g and 93 kcal, which is why the portion looks large for the energy it carries.
Why is theatre popcorn so much higher in calories?
It is popped in oil and often finished with a butter flavoured topping that is largely fat. Air popped corn is the grain alone, near 31 kcal a cup, while theatre butter popcorn can reach 60 kcal a cup or more. Caramel corn adds sugar on top and is higher again.
Can I pop corn without oil?
Yes, in an air popper or in a paper bag in the microwave, and in a covered pan over medium heat with frequent shaking. Without oil the corn is lighter and crisper, but it browns less and carries less flavour, so a light spray of oil after popping is a middle ground.
Is popcorn a healthy snack?
Plain popcorn is a whole grain and a good source of fibre, and a three cup portion is low in energy. The fat, salt and sugar added afterwards decide whether it stays that way. Canada's Food Guide suggests choosing foods with little added sodium and sugar most of the time.