Quality credentials

Why supplement labels state mg, not a percentage: a percentage of what?

A percentage is a ratio, and a ratio is useless until you know what it is a ratio of. "80% carvacrol" is a measurement taken inside the oregano essential oil — at the still, before anyone decided how much of that oil would go into a bottle or how much of that bottle would count as one serving. It is a true statement about an ingredient. A milligram figure is a statement about a serving. That is the whole difference, and it is why the front of a bottle and the back of a bottle so often seem to be discussing different products. The front shouts a percentage because percentages sound like strength. The panel on the back states a weight because a weight is the only thing a laboratory can check and two labels can be compared on.

Why do supplement labels state milligrams instead of a percentage?

Because US labelling rules require an amount, not a ratio — the Supplement Facts panel must give the quantitative amount by weight of each dietary ingredient, per serving.

Under 21 CFR 101.36, the names and quantitative amounts by weight of the dietary ingredients are presented under the heading "Amount Per Serving", in metric units. That much is widely known. The clause that decides this entire page is the one immediately after it: the regulation specifies that the quantitative amount by weight shall be the weight of the dietary ingredient listed, and not the weight of any component, or the source, of that dietary ingredient.

Read that twice, because it is the drafters anticipating exactly the confusion this page is about. The panel is not permitted to describe a product by reference to something upstream of it. A headline percentage is a figure about a component of an ingredient — carvacrol's share of the oregano oil — measured before the finished product existed. The regulation's whole instinct is that a label should state what is in the container per serving, in a unit that does not depend on knowing two other numbers first. The percentage is not banned; it is simply not what the panel is for. It lives on the front of the box, where the rules are looser and the font is larger.

What does "80% carvacrol" actually mean?

It means that about 80 percent of the oregano essential oil's mass is carvacrol — a fact about the oil, not about the bottle and not about a serving.

Between that measurement and the amount a person actually takes lie three multiplications, and the percentage supplies only the first:

1. How concentrated is the essential oil? This is the headline percentage. It is set by the plant, the chemotype, the harvest and the distillation — the ground covered on steam distillation vs cold pressing and wild vs cultivated oregano oil.

2. How much of that essential oil is in the finished liquid? Most liquid oregano oils on the shelf are a small quantity of essential oil diluted into a carrier — usually olive or sunflower oil. This is the number that most often appears nowhere on the label at all. The nearest clue is the "Other ingredients" line, which lists non-dietary components in descending order by weight, so if a carrier oil is named first it is the largest non-active component in the bottle.

3. How much of the finished liquid is one serving? A drop, two drops, a teaspoon, a capsule. And as set out on how to read a Supplement Facts panel, FDA guidance defines a serving as the maximum amount the label recommends per eating occasion — so a label reading "take one to three" must declare a serving of three.

Multiply all three and the result is a mass: milligrams of carvacrol per serving. The percentage is one factor out of three, and the two it omits are the two the manufacturer chose. That is not a scandal — it is just arithmetic. But it means a percentage on its own cannot be read as a strength.

Can two products both labelled 80% carvacrol deliver different amounts?

Yes — and once the middle factor is allowed to vary, the differences become larger than any plausible difference in percentage.

The table below takes four hypothetical bottles, each stating a percentage its maker could defend, and carries the arithmetic through to the share of the finished liquid that is carvacrol. Nothing here describes any particular product on the market; the point is what the numbers do.

The ranking inverts completely. The bottle with the most impressive number on the front holds the least carvacrol per millilitre of anything in the table — about one fifteenth of the bottle with the least impressive number. Every one of those four labels is truthful. Every one describes its oil accurately. And none of them can be compared with any of the others, because they are all quoting the first factor and none of them is quoting the second.

Two honest caveats. These are illustrative dilutions chosen to make the mechanism visible, not measurements of anybody's product; and a share of the finished liquid is still not a serving, because serving sizes differ too. Both caveats point the same way: the further you get from "milligrams of a named compound per serving", the more assumptions you are making on the manufacturer's behalf.

Is a higher carvacrol percentage always better?

Not by itself — a higher percentage means a more concentrated starting oil, which is a real thing, but it is not the same as more of the compound in a serving.

It is worth being fair about this, because the honest version of the argument is more useful than the cynical one. A distiller who reliably produces oil at the top of the reported range has achieved something, and a company that publishes the figure is disclosing more than one that does not. The percentage is a genuine quality signal about the ingredient. The mistake is treating a signal about an ingredient as a measurement of a serving.

And the arithmetic above shows why the mistake is expensive. The spread between a good oil and an excellent one is perhaps 70% to 93% — a factor of about 1.3. The spread between a lightly diluted product and a heavily diluted one is routinely a factor of ten or more. When one lever moves by 30% and the other by 1,000%, ranking products on the first lever is not a close call; it is reading the wrong column. The full context on the percentage itself is on carvacrol percentage: what to look for and what carvacrol is.

Percent by weight, by volume, or by peak area — which one is it?

A bare percentage on a bottle does not say, and the three are not the same number.

Weight versus volume. Percent w/w and percent v/v diverge whenever the components differ in density, and oils do — oregano essential oil is commonly quoted around a specific gravity of 0.94, so a volume ratio and a mass ratio of the same mixture are simply different figures. A label that says "80%" without saying which has left a real ambiguity in place.

Peak area. The more interesting one, and the one almost never mentioned outside a laboratory. Essential oil composition is most often determined by gas chromatography, and GC results are conventionally reported as area percent: each compound's peak as a share of the total detector response, normalised to 100. This is a well-founded convention rather than a sloppy one — where the compounds in a sample are chemically similar, as the aromatic constituents of oregano oil largely are, their detector response factors are close enough that area percent is a good approximation of mass percent. Published work comparing validated methods bears this out; one study quantifying thymol and carvacrol in a thyme oil reported 41.2% and 4.3% by HPLC against 40.7% and 4.2% by GC, agreement close enough to satisfy statistical comparison.

So the point is not that the number is wrong. It is that the number rests on assumptions the label does not state — that response factors are comparable, and that everything present in the sample eluted and was detected. Those assumptions are usually reasonable and occasionally are not. A milligram figure carries none of them, because there is only one kind of milligram.

Is a percentage ever a useful thing to print on a label?

Yes — whenever the label also prints the weight that the percentage applies to.

This is the distinction worth carrying away from the page, and it rescues the percentage rather than dismissing it. "Oregano oil extract 150 mg, standardized to 80% carvacrol" is a genuinely informative line, because the denominator is sitting immediately above it and anyone can finish the sum: 120 mg. The percentage has been given something to be a percentage of.

Standardization is a real manufacturing practice, not a marketing word. It means an extract is produced or adjusted so that a named marker compound falls at a defined level batch after batch — which is a statement about process control, and it gives a laboratory something specific to verify, in the way described on what a certificate of analysis shows. So the rule is not percentages bad, milligrams good. The rule is:

A percentage attached to a stated weight is arithmetic. A percentage floating on its own is an adjective.

Why can't the Supplement Facts panel just show a percentage?

Because the only percentage the panel is built to carry is the percent Daily Value — and botanicals do not have one.

Percent DV expresses an amount as a share of an established daily reference intake, which is why it works for vitamin C, vitamin D, zinc and the rest. Where no Daily Value has been established, the panel must carry a symbol against the line and the footnote "Daily Value not established". Herbs and botanical oils sit squarely in that category, so the percentage column is unavailable to them by design — not withheld, not omitted, simply not applicable.

The consequence is the one that has run through several pages on this site: two botanical labels share no percentage at all. There is no common denominator anywhere on either panel. What they can share is milligrams of a specifically named substance, which is the only unit both are able to express. That is the argument developed on oregano oil for immune wellness and worked line by line on how to read a Supplement Facts panel.

What makes a milligram different from a percentage?

A milligram is fixed by international agreement; a percentage is fixed by whoever chose the denominator.

Since 20 May 2019 the kilogram has been defined by fixing the numerical value of the Planck constant at exactly 6.62607015 × 10⁻³⁴ joule seconds, expressed in units of kg m² s⁻¹ — which, together with the second and the metre, defines the unit of mass. The ampere, kelvin and mole were redefined by fixed constants on the same day, and the last physical artefact was retired from the International System of Units. A milligram is now anchored to a constant of nature. It is the same milligram in every laboratory on earth, and it will be the same milligram in a hundred years.

Percent is not an SI unit at all. It is a dimensionless ratio — a way of writing the number 0.01 — and it carries no information about what it is a ratio of. Its meaning is supplied entirely from outside itself, by whoever decided what counted as the whole. That is not a defect of percentages; it is what they are for. It is only a problem when a percentage is asked to do the job of a measurement.

Which yields the sentence this page exists to hand over: a milligram is a quantity of a thing, and a percentage is a fact about a mixture. Two milligram figures on two different labels are measurements of the same quantity in the same unit and can simply be compared. Two percentages may not even share a denominator.

How do the units compare on a shelf?

Ranked from least to most comparable, the difference is not how strong each phrase sounds but whether two different bottles can be lined up against it.

Read down the last column and the same pattern appears as on what "food grade" means: the claims become more useful as they become less flattering. "93% carvacrol" is designed to be remembered. "18 mg per serving" is designed to be verified — and, crucially, to be capable of being found wrong. A number that could be refuted is a number someone has taken responsibility for.

What does this mean for a bottle of WaveDrops?

It means the label leads with the unit that survives a comparison, and removes the step that makes percentages misleading in the first place.

Each 2-drop serving is stated at about 18 mg of carvacrol and roughly 0.9 mg of thymoquinone — a named compound and a mass. That is the third factor in the chain, already multiplied out, in the unit anchored to the Planck constant. It is also a falsifiable sentence: a laboratory can assay it and find it right or find it wrong, which is not true of a percentage detached from a weight and is not true of an adjective at all. With about 200 two-drop servings in the 0.34 fl oz (10 mL) dropper, that works out at roughly 9 mg of carvacrol per drop, and it implies about 40 drops per millilitre — an arithmetic detour taken properly on how many drops are in a millilitre.

The second half is the more structural one, and it goes to factor two. WaveDrops carries no filler carrier oil — no olive, sunflower, soybean or corn oil added to make up volume. The wild-harvested Greek Origanum vulgare oil and the cold-pressed Nigella sativa oil are both declared actives, so every millilitre in the bottle is the two oils themselves. That matters here for a precise reason rather than a general one: the middle factor is the one nobody prints, and it is the one that swings the answer by an order of magnitude. A product with no diluent has no hidden middle factor to disclose — the concentration cannot depend on how generously a carrier was added, because none was. The product is made in a GMP-certified facility, described here as the floor every US manufacturer has owed since 2010 rather than as a distinction, in the terms set out on the GMP page.

And the honest note to close on, since this page has spent its length arguing that a percentage proves less than people assume: a bottle that states a percentage is not doing anything wrong. An 80%+ carvacrol oil is a real specification and this product states one too. The argument is narrower — that a percentage cannot be compared across brands without two numbers it does not contain, and a milligram per serving can. One is a description of an ingredient. The other is a description of what you take.

Three claims about percentages this page refuses

Stating what is not true is part of stating what is.

"A higher carvacrol percentage means a stronger product." It means a more concentrated oil. Strength per serving is the percentage multiplied by how much oil is in the liquid multiplied by how much liquid is a serving, and the two omitted factors move over a far wider range than the percentage does. As the table above shows, the ranking can invert entirely — which is why a race between headline percentages is a race in the wrong units.

"80% carvacrol means 80% of the bottle is carvacrol." Almost never. The figure describes the essential oil as an ingredient, and most liquid oregano oil products dilute that oil into a carrier before bottling. Unless the label states that the essential oil is the entire contents, the share of the bottle is the percentage multiplied by a dilution ratio that is usually not published. The first name on the "Other ingredients" line is the best available clue.

"Percentages and milligrams are two ways of saying the same thing." They are not convertible without information that the percentage does not carry. A milligram is a mass fixed by the SI since the 2019 redefinition; a percentage is dimensionless and its meaning depends entirely on the denominator chosen, on whether it is by weight, by volume or by chromatographic peak area, and on whether it refers to the ingredient or the finished product. Converting between them requires knowing all of that. Where a label supplies it — "150 mg, standardized to 80%" — the conversion is trivial and the percentage is genuinely useful.

Refusing these three is not an argument that percentages are meaningless or that a company printing one is being evasive. Standardization is real process control, a published carvacrol figure is a real disclosure, and an analytical result reported as area percent is a real measurement made by a real instrument. The argument is only this: a percentage is a fact about a mixture and a milligram is a quantity of a thing, and only the second answers the question a person holding two bottles is actually asking. Which gives the four-second test — find the number that has a unit of mass and the word "per serving" next to it. If there isn't one, you have been given a ratio and asked to supply the rest yourself.

Related reading: how to read a Supplement Facts panel, carvacrol percentage: what to look for, how many drops are in a millilitre, what a certificate of analysis shows, and how to choose a quality oregano oil. Or return to the WaveDrops homepage.

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These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.