Nutrition label rounding: the rules, and why labels never add up

What is nutrition label rounding?

Every number on a US Nutrition Facts panel has been rounded, and not to a single scale. Calories go up in fives to 50 and in tens after that. Fat below five grams moves in half-gram steps and in whole grams above. Sodium under five milligrams is printed as zero. Cholesterol rounds to the nearest five. Even the servings-per-container line has a rule of its own, with half-serving steps between two and five and whole ones outside.

All of it is set out in 21 CFR 101.9(c), the section of the Code of Federal Regulations that tells a manufacturer what a label must say. It is not guidance and it is not house style: the increments, the thresholds and the boundaries are written down, and this page implements them from the regulation's own text.

The reason it matters is that a rounded number and a measured number are different things. A label saying zero grams of trans fat is making a claim about a threshold, not reporting a measurement, and a label whose calories do not equal nine times the fat plus four times the carbohydrate plus four times the protein is not making a mistake. Both of those follow from the rules, and this tool shows them happening.

How to use it

1. Enter the real amounts in one serving. The unrounded figures — what a laboratory measures, before anything is rounded for print. The sample buttons load five servings, each built to show a different part of the rules.
2. Read the panel on the right. That is the label the regulation requires for the amounts you entered, with each nutrient rounded by its own rule. Percent Daily Values are deliberately left out: they are a separate calculation from the rounding this page is about.
3. Read the three sections below it. One compares the calories three ways and shows the gap. One lists every nutrient your serving contains that the label must print as zero, per serving and across the whole container. One says whether your calories land near a value no label can print.

The label is not designed to add up

Multiply the grams on a real label by nine, four and four and you will usually not get the calories printed beside them. This is the single most common reason people think a label is wrong, and it is the rules working exactly as written.

The regulation settles it in one clause. Where calories are calculated from the macronutrients, 21 CFR 101.9(c)(1)(i) requires that the factors "shall be applied to the actual amount (i.e., before rounding) of food components". So the calories come from the unrounded grams and are then rounded on the calorie scale, while each gram figure is rounded separately on its own. Two independent roundings cannot be expected to reconcile.

Measured across two hundred thousand servings, multiplying the printed grams lands exactly on the printed calories about one time in twelve. Four times in five it is within five calories, and the worst gap in that sweep was twelve. So the arithmetic is usually close, occasionally noticeably off, and never guaranteed — which is a much more useful thing to know than a rule of thumb.

Two things the printed numbers cannot tell you

The first is what a zero contains. Under half a gram of any fat prints as zero; under five milligrams of sodium prints as zero; under two milligrams of cholesterol prints as zero. Those are thresholds, so a serving with 0.45 grams of trans fat and a serving with none are printed identically. The servings-per-container figure is on the same label, so the container arithmetic needs nothing you do not already have: eight servings at just under half a gram is just under four grams, all of it declared as zero. This tool does that multiplication for you.

The second is that some printed values do not exist. Because calories move in fives up to 50 and tens above it, 55 is not a number a US label can legally carry — nor 65, 75, 85, or any other odd multiple of five above fifty. There are 195 such gaps below 2000 calories. Sodium has exactly the same hole above 140 milligrams. It is worth checking a few packets: you will not find one.

There is a pleasing consequence of how the boundaries are written. The regulation says calories round to the nearest five "up to and including 50" — and that phrase turns out to change nothing at all, because 50 is a multiple of both five and ten, so both rules agree there. The same is true of fat at five grams, sodium at 140 milligrams and the servings window at two and five. Every boundary the regulation names is a multiple of both increments it separates, so whether the endpoint is included is unobservable.

Honest limitations

The regulation says to round "to the nearest" increment and never says what to do with a value sitting exactly halfway between two of them. This page rounds halves away from zero, matching what a spreadsheet's ROUND does, and states that rather than implying the question is settled. If you reproduce a boundary case by hand and get the other answer, neither of us is wrong about the regulation.

These are the US rules, as published in the 2025 edition of the CFR. Other jurisdictions round differently and require different nutrients altogether, so a number from one label is not comparable with a number from another country's. The CFR is revised annually; the page prints the edition it was built from, and the tests that verify it assert each rule against the sentence of the regulation that states it, so a revision that changes a rule breaks the build rather than quietly making this page wrong.

Finally, this page is about rounding and nothing else. It does not calculate Percent Daily Values, does not decide serving sizes from the reference amounts in the same regulation, and takes no view on whether any of the thresholds are set at the right place. It shows you what the arithmetic does, which is a smaller claim than most pages on this subject make and one you can check line by line.

Why is it free?

It is a dozen conditional roundings, and your browser does the lot as you type. No server is involved, so there is nothing to meter and no account to create.

Nothing is uploaded. The numbers you enter stay in this tab.