Calories are most common in the United States when discussing food, but we’ve managed to muck up the standard usage. One calorie is defined as the energy needed to raise the temperature of one milliliter of water (one-fifth of a teaspoon) by one degree Celsius (1.8 degrees Fahrenheit). It’s a tiny amount of energy—too small to be a useful unit of measure when we talk about food (like road signs giving driving distances in inches). Instead, when we talk about “calories” in food, we’re actually talking about kilocalories, or 1,000 calories. A cup of dry Cheerios has 100 calories according to the
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