Taco Bell sells four tacos that are purely hard shell. Calorie contents vary depending on the amount of meat and cheese included, choice of sauces and shells, and fat-laden additions such as sour cream.

If you approach the counter and simply ask for a “hard taco,” you will likely be offered the crunchy taco. This basic taco includes seasoned beef, lettuce and cheese. At 170 calories, this option isn't the healthiest on the menu, but it won't undo your whole day either.

The Fresco Crunchy Taco substitutes a hearty, veggie salsa for the cheddar cheese of a normal hard taco. The result is a taco with only 150 calories, according to Taco Bell . This is just 7.5 percent of your daily recommended caloric intake, according to MayoClinic.com.

The Taco Supreme is a hard shell taco that adds tomatoes and sour cream to the standard beef, lettuce and cheese. While Taco Bell uses low-fat sour cream, this addition still adds some extra calories, and at 200 calories, this hard taco is 10 percent of your daily recommended values.

Taco Bell's Volcanic Taco is the most fattening hard taco option. This spicy menu item provides 240 calories. If you want a spicy taco without the extra calories, consider adding Taco Bell's “Fire” Boarder Sauce to the Fresco Crunchy Taco. These spicy sauce packets are complimentary, and they contain zero calories.