How to count calories from a photo (and get a better estimate)

Snapping a photo of your plate is the fastest way to keep a food diary. You don't weigh anything, search a database or type. Apps like Biscai look at the picture, recognise the foods and estimate the portion, calories and macros in a few seconds.

A photo, though, is a flat picture of a three-dimensional meal. Once you know what the camera can and can't see, a rough guess becomes a number you can work with.

What happens when you snap your plate

Photo-based calorie counting comes down to three questions:

1. What is on the plate? The AI identifies each food: grilled chicken, rice, a side salad, a slice of bread.
2. How much of each? It estimates the portion from visual cues: the size of the plate, how much of it each food covers, how high the food is piled, and familiar objects like a fork or a glass.
3. How energy-dense is it? Each food has a typical number of calories per 100 g. Multiplied by the estimated weight, that gives calories, protein, carbs and fat.

The first step is usually the easy part. Most of the uncertainty sits in the other two: how big the portion is, and what went into the food before it reached the plate.

What a photo can't see

• Oil and butter. A tablespoon of olive oil has about 120 kcal, and it disappears into a stir-fry or a salad. Two meals that look the same can differ by a few hundred calories because of what happened in the pan.
• Sauces and dressings, especially underneath. Dressing soaked into a salad or sauce under the rice is hard to spot.
• Depth. A deep bowl and a shallow plate can hold very different amounts and still look alike from above.
• What's inside. The filling of a wrap, a pie or a sandwich is mostly hidden.
• Drinks. A latte, a juice or a glass of wine next to the plate is easy to leave out of the photo, and then out of the diary.

This doesn't mean photo counting doesn't work. It means the photo needs a little help.

8 habits for a better estimate

1. Shoot at an angle, about 45°. Straight from above hides the height of the food; from the side hides the plate. An angle shows both.
2. Get the whole plate in the frame. The edge of the plate is a useful size reference.
3. Leave a fork or spoon in the picture. A familiar object helps judge scale.
4. Use good light. Daylight or a bright room makes it easier to tell rice from cauliflower, or a cream sauce from yoghurt.
5. Photograph before you eat. Then log what you leave instead of guessing what was there.
6. Add what the camera can't see. If you cooked with a generous splash of oil or added butter, log it.
7. Log your drink. Biscai asks whether you had a drink with each meal, so it doesn't get forgotten.
8. Correct the portion when you know better. Ate only half, or went back for seconds? Adjust it after the meal.

Precise or consistent?

A kitchen scale is more accurate than any photo. But weighing every meal takes time, and plenty of people give it up after a while. A diary you've stopped keeping doesn't help anyone.

Photo counting trades a little precision per meal for something more useful: logging every meal. Over weeks, the trend of what you eat and how your weight changes tells you more than any single number. If your weight isn't moving the way you expected after two or three weeks, adjust your daily target.

When precision really matters, for example in baking or when following a plan from a dietitian, weigh your food. For everyday meals, a good photo and a quick check are usually enough.