How to Calculate the Calorie Content of Food

There is no single method that works for every situation — a combination of approaches gives you the most reliable picture.

Reading nutrition labels

Pre-packaged foods carry a nutrition information panel showing kilocalories (kcal) per 100 g and often per serving. The per-100 g figure is the most useful when you are weighing food yourself, because it lets you scale the number to exactly how much you are eating. Weigh the portion, divide the weight by 100, then multiply by the kcal per 100 g figure on the label.

Example: a food with 180 kcal per 100 g, and you eat 75 g: (75 ÷ 100) × 180 = 135 kcal.

Using a food database

For unpackaged or restaurant food, a searchable food database gives you a per-100 g or per-portion calorie figure you can apply the same way. General educational values for common whole foods — such as a medium egg being roughly 70–80 kcal, or a teaspoon of olive oil around 40 kcal — are widely published, but always treat database values as estimates rather than precise facts, since preparation methods and ingredient variations do affect the final figure.

Weighing and tracking consistently

Accuracy improves significantly with a kitchen scale. Estimating portions by eye tends to undercount, especially for calorie-dense foods like nuts, oils, and cheese. Logging the weight alongside the kcal-per-100 g figure keeps your totals honest.

Once you have a calorie total, you can use it alongside broader measures of your intake — which is where understanding your calorie deficit or knowing how to calculate your macros becomes useful. Together, calories and macros give you a fuller picture than any single number. If you are curious how your intake relates to your broader goals, our calorie calculator hub covers the key concepts in one place.

Manually calculating every meal from first principles is accurate but time-consuming — and on a GLP-1 journey, meal sizes and appetite can shift quickly, making it easy to fall behind on logging. GLP Trackr's AI food photo scan is designed for exactly this: point your phone camera at a meal and get an instant calorie and protein breakdown without touching a spreadsheet.

For packaged foods, the barcode scanner pulls nutrition data automatically. If you prefer to search by name or enter details manually, that option is there too. The app rolls your entries into daily totals against your calorie and protein targets, so you can see at a glance where you stand — useful when smaller, protein-focused meals are part of how you are eating while on your medication.

You can also see how your calorie intake relates to your progress over time using the app's insights features, which surface patterns across your own data. If you want to understand your results in the context of your wider journey, pairing calorie data with weight progress tracking gives you a much clearer view than either alone.

GLP Trackr is free to download on the App Store and Google Play, with a 7-day trial — snap a photo of your next meal and see how easy calorie tracking can be.