In technical usage, 1 kilocalorie is equal to 1,000 calories. The terms are subject to some confusion, however, since in popular speech "calorie" and "kilocalorie" are often used interchangeably. Wikipedia explains that this confusion has motivated some writers and scientists to capitalize "Calories" for kilocalories, as a way of distinguishing between the two.
According to the University of Texas at Arlington, technically defined, 1 calorie is the amount of energy required to raise the temperature of a single liter of pure water by exactly 1 degree centigrade. Metric naming conventions dictate that the prefix "kilo" should be applied to any group of 1,000 smaller units.
In scientific literature, this convention is rigorously adhered to, but popular publications and advertisements have blurred the distinction in the public discourse. A "400-calorie" meal, for instance, is actually 400 kilocalories, or 400,000 calories. The daily intake requirement for a healthy adult is around 2,200 "Calories," which is actually 2.2 million calories.
University of Texas at Arlington explains that fitness charts also blur the distinction between calories and kilocalories. A table showing the number of calories expended in half an hour of vigorous exercise often express kilocalories in "Calories," as a way of making the information accessible to a non-technical audience. The same table, published in peer-reviewed literature, uses the more accurate "kilocalorie" metric terminology.