How Bites estimates calories from a photo

What happens when you take a photo

1. You take the photoBites shrinks it to at most 1,024 pixels and removes location and camera data before it leaves your iPhone.
2. The model looksAn AI model on Cloudflare Workers AI names each visible food and estimates its portion in grams, using the plate, cutlery or your hand for scale.
3. The database checksEach food is looked up in the Bites food index. When a close match is found, its nutrition per 100 g replaces the model's numbers.
4. Each item is labelledHigh confidence, Estimate or Rough guess, with a note on the biggest source of doubt.
5. You decideChange a name or the grams, remove an item or add one that was missed, then log it.

If the main model is busy, slow or gives an answer that doesn't fit the expected format, a backup model on the same service answers instead. The model is also told never to add foods it can't see.

Where the numbers come from

The model's main job is to say what each food is and how much of it there is. For calories and nutrients, Bites prefers a food database:

• Bites searches its food index for each item, first by a plain generic name (for example “grilled salmon fillet”), then by the name you see.
• Only foods from USDA FoodData Central and foods we curated ourselves are used, and only when the database's calories per gram are within 20% of the model's own figure. This is a matching rule, not an accuracy figure: it stops a similar-sounding name from swapping in a very different food.
• When there is a match, Bites multiplies the database's nutrition per 100 g by the portion from the photo. The portion always comes from the photo.
• When there is no close match, the model's own numbers are used, and the confidence label tells you how far to trust them.

So a database can't fix a wrong portion. If the model sees 150 g of rice and there are 250 g, the calories are low by the same proportion. Portions are the first thing to check.

What the confidence labels mean

The model rates each item high, medium or low. The rating is about the portion more than the name: a food can be easy to recognise and still hard to weigh. Bites shows it as a label with an icon and a colour:

• High confidence

  The portion has clear edges: a packaged item, a whole piece of fruit, a standard slice.

• Estimate

  The food is clear, but the amount or the way it was cooked could vary. Worth a look at the grams.

• Rough guess

  Mixed dishes, sauces, oil and anything partly hidden. Check these items first.

On the Today screen, entries that are less than sure keep a small Estimate or Rough guess label after you log them, so you can come back and correct them.

Where photo estimates go wrong

A photo shows the surface of a meal, and some things it simply can't see. These are the usual reasons an estimate is off, and what to do about each.

Restaurant meals combine all four: more fat than you'd expect, portions you can't weigh and sauces you can't see. Treat the result as a starting point and adjust what you know.

How to correct an estimate

• Before you log: tap any name or amount on the result. Each food has a grams slider, and you can remove items or add one that was missed.
• Tell Bites what it really is: under “Something's off?”, describe the meal in your own words and choose Re-estimate. The photo is analysed again with your hint.
• After you log: open the entry to change its name, grams, calories, protein, carbs, fat, fiber, sugar or sodium, or delete it.
• In a planned meal: Swap replaces an item with a food from the database, and its nutrition per 100 g replaces the estimate.

Whatever you log is kept as one of your own foods, with the numbers you set, so next time you can find it in search. A later estimate never overwrites a number you typed.

When you correct a result, the app sends the model's answer and your corrected version to our server, without the photo, so we can measure and improve the estimates.

Other ways to log, and where their numbers come from

How your daily calorie budget is set

• Bites estimates your resting energy with the Mifflin-St Jeor equation (sex, age, height and weight), then multiplies it by an activity level between 1.2 and 1.7 for everyday movement.
• To lose or gain weight it subtracts or adds energy at about 7,700 kcal per kilogram, with losing capped at 1 kg a week and gaining at 0.5 kg a week.
• The budget never goes below a floor: 1,200 kcal for women, 1,500 kcal for men and 1,350 kcal if you'd rather not say.
• Training you plan or record adds its energy on that day, and Apple Health workouts are counted once.
• Once you have 14 complete days and 6 weigh-ins within 28 days, the weekly check-in compares what you ate with your weight trend and may suggest moving the budget by up to 150 kcal. You choose Keep or Apply.

How accurate is it?

We don't publish an accuracy figure yet, because we haven't measured one we would stand behind. A fair test needs a set of weighed meals, photographed in ordinary light on ordinary plates. When we have run one, the method and the results will be on this page.

Until then, the honest answer is this: the estimate is good at telling you what's on the plate and roughly how much, and weakest on hidden fat and portion size. The labels tell you which items need a look, and every number can be changed.

What happens to your photo

• Before it leaves your iPhone, the photo is shrunk to at most 1,024 pixels and stripped of location and camera data.
• It is analysed in memory by AI models that Cloudflare runs for us, and it is not stored on our server. Cloudflare doesn't use it to train AI models.
• The result, not the photo, is kept for 15 minutes so that a retry after a dropped connection doesn't cost a second analysis.
• A small thumbnail stays on your iPhone with the entry.
• The body photo features are separate: off by default, for adults only, and they ask before anything is sent.

The privacy policy lists every service involved and what each one receives.

Bites is not medical advice

Estimates are for information, not diagnosis or treatment. If you're managing a medical condition, are pregnant, or have a history of disordered eating, talk to a doctor or dietitian before you use any calorie tracker.