In this guide
Compare the same amount
Before comparing two nutrition numbers, check how much food each number describes. A cereal with less sodium per listed serving can have more sodium when you compare the same weight of food.
The method is simple: check the serving, choose an equal amount, then adjust the numbers. The worked example below shows how—and where the calculation has limits.
Start at the serving information
US Nutrition Facts labels generally give nutrient amounts for one serving. Some also have a whole-package column, so check the heading above the numbers. The serving size reflects an amount people typically consume; it is not a recommendation for how much you should eat. One package may contain several servings. FDA serving-size guidance.
For similar dry foods, the weight in grams gives you a common basis even when the household measures differ. Compare dry cereal with dry cereal. If one column includes milk or describes a prepared food, it answers a different question. Check the food form as well as the weight before doing any math.
Two servings, two different amounts
These are invented cereal values for a math exercise, not measurements of real products. The table shows selected nutrients, not complete Nutrition Facts labels.
On a small screen, scroll sideways to read the full table.
| Listed information | Cereal A | Cereal B |
|---|---|---|
| Serving weight | 30 g | 45 g |
| Sodium per serving | 150 mg | 180 mg |
| Fiber per serving | 3 g | 4 g |
A's sodium number looks smaller: 150 mg versus 180 mg. But A's number describes only 30 g of food; B's describes 45 g.
Let's compare 45 g of each cereal. This is a convenient comparison amount, not a recommended portion.
For A, divide the comparison weight by its listed serving weight:
45 ÷ 30 = 1.5 servings
Then multiply each nutrient amount by 1.5:
- Sodium: 150 × 1.5 = 225 mg
- Fiber: 3 × 1.5 = 4.5 g
B's serving is already 45 g, so its multiplier is 1 and its numbers stay the same.
On a small screen, scroll sideways to read the full table.
| Calculated for 45 g of each | Cereal A | Cereal B |
|---|---|---|
| Sodium | 225 mg | 180 mg |
| Fiber | 4.5 g | 4 g |
On this arithmetic, A has a higher estimate for both sodium and fiber. We have answered two nutrient questions; we have not ranked the cereals' overall healthfulness. A single nutrient number cannot describe everything someone may consider when choosing food.
This calculation applies the FDA's explanation that nutrient amounts change in proportion to the number of servings. FDA label guide.
Use this formula with another label
First calculate the multiplier:
Comparison weight ÷ listed serving weight
Then calculate the nutrient amount:
Listed nutrient amount × multiplier
Use matching units for the two weights: grams with grams, for example. Keep the nutrient's unit too—milligrams of sodium remain milligrams. A phone calculator is fine.
Label values are rounded. For example, the US rules specify rounding increments for sodium and fiber. Multiplying a displayed value does not recover the unrounded amount. Treat the results as estimates for comparison, and avoid reading too much into a small difference such as the half-gram fiber gap above. Nutrition-label rounding rules, sections (c)(4) and (c)(6)(i).
If a label says “less than 1 g,” it has not supplied an exact number to multiply. Keep that limitation visible rather than silently treating it as either zero or one.
Equal weight or the portion you plan to eat?
Those are two useful questions with different denominators—the amounts behind the numbers.
- Equal weight: What would each food contribute at the same weight? This is the question our 45 g comparison answers.
- Planned portions: What would each contribute in the amount you actually intend to eat? Calculate each portion separately, then name those amounts beside the results.
For example, if you plan to eat 30 g of fictional cereal A and 45 g of fictional cereal B, the starting table already describes those portions. A then contributes an estimated 150 mg sodium and B 180 mg. That does not contradict the equal-weight result; the question changed.
Before comparing prepared foods, check whether both labels include the same additions. A column for cereal alone and one for cereal plus milk should not be treated as equivalent. US label-format rules, section (e).
What about percent Daily Value?
Percent Daily Value, or %DV, compares a nutrient amount with a daily reference. FDA's general guide is 5% DV or less is low and 20% DV or more is high, per serving. These percentages need the same serving-size attention as grams and milligrams. They are label-reading references, not a personalized nutrition plan. FDA Daily Value explanation.
Try it yourself
Two imaginary crackers list:
- Cracker A: 90 mg sodium per 20 g
- Cracker B: 120 mg sodium per 30 g
Which has less sodium when you compare 30 g of each? Try the multiplier before reading the answer.
Answer: A's multiplier is 30 ÷ 20 = 1.5, so its estimate is 90 × 1.5 = 135 mg. B's multiplier is 1, giving 120 mg. B has the lower calculated sodium amount at equal weight, even though its original per-serving number was larger. These are fictional teaching values, and 30 g is not a portion recommendation.
For your next comparison, write down four things: food form, amount, nutrient and unit. Once those match, the numbers are much easier to interpret.
About this article
Edited by Tony Lewis. Editorial review: October 29, 2026.
