Barcode scanner calorie counter: from the stripes on a pack to your portion

How does scanning a barcode for calories work?

The stripes on a pack encode a product number, usually 13 digits in Europe and Turkey. The barcode itself holds no nutrition at all; it's simply an ID. The rest happens in three quick steps:

1. The camera reads the number. No typing, and no scrolling through ten products with similar names.
2. The app looks it up. Doydum checks Open Food Facts, an open, collaborative database where volunteers add products and their label values from around the world.
3. You get values per 100 g (or per 100 ml for many drinks): calories, protein, carbs and fat, ready to scale to your portion.

Doydum keeps a copy of products it has already looked up, so scanning your usual yogurt again is quick. Coverage varies by country and brand: widely sold products are more likely to be there, while local, new or small-batch ones can be missing. That's where Ask AI comes in, further down.

A few habits make scanning smoother: find decent light, hold the phone steady for a second while the camera focuses, smooth out crumpled wrappers, and turn round bottles and jars until the stripes face you flat.

How to read a nutrition label

Most labels in Europe and Turkey use the same rows, per 100 g or 100 ml:

• Energy, given twice: in kilojoules (kJ) and kilocalories (kcal). The bigger number is the kJ one; 1 kcal is 4.184 kJ. Calorie counters, Doydum included, use kcal.
• Fat, with saturates listed underneath as part of it.
• Carbohydrate, with sugars listed underneath as part of it.
• Protein and salt, and sometimes fibre.

The "of which" rows are already inside the line above, so don't add them on top. For your log, the four numbers that matter are calories, protein, carbs and fat, and that's exactly what a barcode scan brings in.

Why are barcode values per 100 g?

Because that's how most labels in Europe and Turkey present them, and it makes products easy to compare. 100 g of one yogurt against 100 g of another is a fair comparison; "one pot" against "one serving" isn't.

The catch is that nobody eats exactly 100 g of everything. So the number that matters is always value per 100 g × grams eaten ÷ 100. A calorie tracker with a barcode scanner does this sum for you, as long as the grams are right.

Many labels also print a "per serving" column. It's handy, but check what the maker means by a serving: it may be smaller, or bigger, than what ends up in your bowl. If a 500 g tub of yogurt lists a 150 g serving, eating the whole tub is more than three servings.

How to work out your portion from a label

Take a 200 g pack of plain biscuits. Say the label gives, per 100 g: 443 kcal, 6.5 g protein, 71 g carbs and 15 g fat. Here's what different portions come to:

For 40 g: 443 × 40 ÷ 100 = 177.2, so about 177 kcal. The same sum works for every macro. Notice how much the answer depends on the grams: the database can be spot on and your log still be off if the portion is a guess. If you can, check the pack weight, or weigh your portion once or twice until your eye learns.

What if the barcode isn't found?

Every database has gaps, especially for local products, new flavours and small brands. When a scan comes back empty, Doydum offers Ask AI:

1. Photograph the pack, ideally with the nutrition table in view, or at least the name and brand.
2. If the nutrition table is visible, the AI reads the values straight off the label.
3. If it isn't, it searches the web by the product's name and brand.
4. If neither works, it gives a clearly labelled estimate.

Either way, it tells you which of the three it did, so you know how much to trust the numbers. An estimate is still an estimate: compare it with the pack and adjust the portion before saving. For food without packaging, a photo of the plate works better; see our guide to the AI calorie counter.

Pack weight and portion chips: getting the grams right

With packaged food, the amount is usually the trickiest part. Doydum makes it quick:

• Pack weight first. When the pack weight is known, the portion starts at the whole pack. For a single bar, a small pot or a can, that's often exactly right.
• Portion chips. Ate part of a bigger pack? Tap a chip to change the amount in one go instead of typing.
• Your own grams. Weighed it? Adjust the grams to match.

Before saving, glance at the calories. If a quick snack shows the whole family-size pack, the portion is the first thing to check.

Label vs serving: what to double-check

• Per 100 g or per serving? Make sure you're reading the right column, and that the numbers you log match it.
• As sold or as prepared? Dry foods change weight when cooked. Rolled oats are 379 kcal per 100 g dry, so weigh them before the milk or water goes in. Cooked pasta is 158 kcal per 100 g because it has soaked up water.
• Drinks per 100 ml. A 330 ml can is 3.3 times the label value.
• Does the entry match the pack? Recipes change and database entries can be out of date. If the numbers on the pack in your hand differ, trust the pack and save it with the label's values as one of your own foods.
• Right variant? Light, full-fat and flavoured versions of the same product have different barcodes, so scan the pack you're actually eating from.
• Multipacks. The barcode on the outer wrapper may describe the whole box, not one bar inside it.

Barcode or photo: which should you use?

Use the tool that matches the food:

For packaged food, scanning the barcode usually beats photographing it on a plate, because the numbers come from the label rather than from an estimate. Mixed meals use all three. A breakfast might be a scanned yogurt, a typed simit and a photo of a pan of menemen. For getting the whole day right, read how to count calories, or see the scanning features on our home page.

Questions people ask