Here are some specific examples of online calorie calculators that you can use to track calories in food:
MyFitnessPal: This popular website and mobile app allows you to track your calorie intake by searching for foods in their database, and also allows you to input the nutritional information for custom or homemade meals.
Livestrong's MyPlate: This is a mobile app and website that allows you to track your calorie intake, set goals and also give you an idea on how to balance your macro and micronutrients.
Fatsecret: This is a website that features a food diary and a calorie counter, as well as a variety of tools to help you track your nutrient intake and monitor your weight loss progress.
Sparkpeople: This website offers a number of tools to help you track your calorie intake, including a food diary, a calorie calculator, and a database of nutrition information for thousands of foods.
Cronometer: This is an app that allows you to track your food intake and calories. It also gives you a breakdown of macronutrients and micronutrients. You can also scan barcodes to get nutritional information of packaged food.