Calculate a concentrate after adding water
Track concentrate quantity, final mixed volume, and poured portion so dilution changes concentration without changing the batch total.
Dilution changes how much of a nutrient appears in each millilitre of a drink. It does not by itself change the amount supplied by the concentrate you used. Keep the total for the mixed batch separate from the concentration of that batch.
The EU food information regulation allows appropriately described prepared-food information. Check whether a concentrate's panel already gives values after dilution before doing another conversion.
Use final volume rather than guessing from the bottle
Imagine a fictional concentrate contains 60 g sugars per 100 ml. You measure 25 ml of concentrate and mix with water to a final volume of 250 ml. Assume the water adds none of the nutrient being calculated and the concentrate is fully transferred.
The concentrate contributes 60 × 25 ÷ 100 = 15 g sugars. That remains the estimated total in the mixed batch. Per 100 ml of finished drink, the amount is 15 ÷ 250 × 100 = 6 g.
A 150 ml glass poured from the well-mixed batch therefore contains 6 × 150 ÷ 100 = 9 g sugars. The other 100 ml contains 6 g. Adding the two portion amounts returns the original 15 g batch total.
Distinguish two possible mixing directions
“Add water to make 250 ml” specifies the final volume. “Add 250 ml water” specifies only the water added. Those are different instructions. For the second instruction, the finished volume is not established by the phrase alone, and casually reusing 250 ml as the final denominator would be wrong.
Measure the final mixture or follow a manufacturer-provided yield. Do not assume a dilution ratio has the same meaning across products; some describe concentrate-to-water parts, while others describe a final serving.
What if the drink is stronger?
If the same 25 ml concentrate makes only 200 ml final drink, the total is still 15 g, but the concentration becomes 7.5 g per 100 ml. A 150 ml glass then contains 11.25 g. The change comes from the smaller final volume, not an extra ingredient.
Record concentrate amount, final volume, and poured volume together. This makes the estimate reproducible and prevents a prepared-drink value from being mistaken for a concentrate value in a later comparison.