Use per 100g to compare concentration
Imagine Bar A contains 15g of protein in a 50g serving. Bar B contains 18g in a 60g serving. Bar B supplies more protein when you eat the whole thing, but both contain 30g of protein per 100g. The difference comes from the portion size.
This is why a larger front-of-pack number is not enough to judge a recipe. Place products on the same weight basis before comparing their protein, sugar or energy figures.
Use per bar to plan your snack
Once you have compared the recipes, consider what you will eat. If you take one wrapped bar to work, the per-bar numbers are the relevant ones for that snack. If a packet contains two servings, check whether the advertised figures refer to one serving or the whole packet.
Do not assume every product described as a bar has a similar weight. The portion is part of the product design, just like its flavour or texture.
Do the calculation in either direction
To convert a per-bar amount into a per-100g figure, divide it by the bar weight in grams and multiply by 100. For the hypothetical 50g bar above, 15 ÷ 50 × 100 = 30g protein per 100g.
To work backwards, multiply the per-100g figure by the portion weight and divide by 100. A 40g portion of that same recipe would contain 12g protein. These calculations also work for sugars and calories. Small differences may appear because labels round their values.
Keep the comparison useful
A fair comparison needs the same nutrient, the same basis and the current label. Compare sugars with sugars, not sugars with total carbohydrate. Avoid mixing figures from different flavours or older versions of a recipe.
Try a simple shopping note: product, portion weight, protein per bar, sugars per bar and price. Add per-100g figures when the sizes differ. You will have a clearer picture than a ranking based on one headline claim.