Serving Scaler Calculator.
Scale the label to the portion you actually eat. I use the serving size and nutrition values on your package.
Fill in the form and your result lands here.
Learn the details
How it's figured
This is arithmetic on the numbers you supply, not a food database or a validated nutrition assessment. I divide your portion weight by the label serving weight, then multiply the label calories, protein, carbs and fat by that factor. Both weights stay in grams.
I would check that the label and your portion describe the food in the same state, such as both dry or both prepared. Include any milk, oil or other additions separately. The label serving is a reference for the calculation, not a rule for how much to eat.
Why it's an estimate
I use the serving on the label as a reference for arithmetic. It is not a rule for how much you should eat. Weigh your portion, enter the values from your package, and I scale them to the amount you have.
Match the label to the food
I would check whether the label describes dry, raw or prepared food before weighing a portion. Both weights need to describe the same state and be in grams. Include milk, oil and other additions separately. Both weights must be above zero; a label value such as fat or protein can be zero.
A worked example
The prefilled example is a 65 g bowl of cereal with a label serving of 30 g. The example label lists 120 calories, 4 g protein, 22 g carbs and 2 g fat per serving. I divide 65 by 30 to get the multiplier, about 2.1667. Multiplying each label value by that unrounded factor gives 260 kcal, 8.7 g protein, 47.7 g carbs and 4.3 g fat after display rounding. Any milk is separate.
The servings display reads 2.2, but I keep the full multiplier for the calculation. Using the rounded 2.2 to redo the arithmetic would give a different answer. I round calories to a whole calorie and nutrients and servings to one decimal.
Keep the precision in perspective
I use the calories you enter from the label, rather than rebuilding them from protein, carbs and fat. Label values may already be rounded, so the scaled numbers are only as precise as those inputs. This is not a food database or a separate assessment of what is in the food.
When I would update the result
The same label and portion give the same answer next week. I would recalculate when the portion changes or a new package has different nutrition values or serving sizes. There is no timed recheck for a result whose inputs have stayed the same.