1 Snickers Snickers Bar (15 g) contains 80 calories (Fun Size). Calorie breakdown: 43% fat, 50% carbohydrates, and 7% protein. The amount of calories in a Snickers bar depends on the size of your bar and how you cook it. A small bar (50 grams or 1.75 oz) has about 280 calories; a medium bar (55 grams or 2 oz) has about 310 calories; and a large bar (70 grams or 2.5 oz) has about 340 calories. To burn off those calories, you would need to walk for 3 hours straight with no breaks. Otherwise, you might as well sit through that movie instead. Calories are the body's source of energy. You need food to live and eat whatever else you want is just an option. However, eating too much can lead to obesity which is another term for having too much fat inside your body. Eating too much added sugar can also be very harmful to your health. So, the first thing you should know about calories is they are your body's source of energy. Without them, you would die after a few days because your body wouldn't have enough power to keep itself going.