2,400 mcg of S-allyl cysteine is exactly 2.4 mg. Same quantity, two ways of writing it. The common mg vs mcg error is comparing the total extract weight instead of the standardised marker, and 1,000 mg or 1,200 mg of aged garlic extract describes the carrier material around the marker rather than the marker itself.
Cysteine unit arithmetic is one move, done once
There are 1,000 micrograms in one milligram, so going from mcg to mg means dividing by 1,000. Going the other way means multiplying by 1,000. That is the entire operation. Where people lose the plot is applying it halfway: they see 2,400 mcg on one bottle and 2 mg on another, decide the first one is bigger because 2,400 looks bigger than 2, and buy it. It's technically bigger by 0.4 mg. Whether that matters depends on why you are taking it, not on how large the digits look.
You'll be able to run this on any label in a few seconds. Find the nutrient or marker line, not the ingredient weight line. If one bottle says 2.4 mg SAC and another says 800 mcg SAC, divide the second by 1,000 and you get 0.8 mg. The first delivers three times as much marker per serving. Now you are comparing something real.
Here is a worked table using figures that actually appear on aged garlic labels:
| Label line | As written | In mg | In mcg |
|---|---|---|---|
| SAC, standardised | 2.4 mg | 2.4 | 2,400 |
| SAC, standardised | 800 mcg | 0.8 | 800 |
| Total aged garlic extract | 1,200 mg | 1,200 | 1,200,000 |
Notice the third row. Converting correctly shows the total extract outweighs the marker by roughly 500 to 1, which is the normal relationship in an aged preparation. The extract carries the SAC; the SAC is the part the research measures.
Why the microgram line exists at all
Micrograms exist because some nutrients are needed in amounts too small for milligrams to be readable. Vitamin B12 lands in this group, along with folate, biotin and selenium. Nobody wants to read 0.0024 mg on a panel. Laboratories and regulators settled on the microgram so the numbers stay whole. Vitamins A and D complicate this further still by having a third unit, the IU, which describes biological activity rather than weight. You can't convert IU to mcg with plain arithmetic. Specific nutrients have specific conversion factors, and those factors differ between nutrients. If a label offers only IU and you need micrograms, that is a case for finding a better-labelled product rather than doing sums.
What you should actually compare
Pick one unit and stay in it. Milligrams work for most supplement comparison because most markers of interest are dosed in that range.
Then compare per serving, not per bottle. A 120-count bottle where you take two is a 60-day supply. A 90-count bottle where you take three is a 30-day supply. The cost per day is the honest number, and it changes the ranking of two bottles more often than the milligram figure does.
Regulators give you a reference point for all of this. The NIH Office of Dietary Supplements publishes fact sheets for most nutrients, and each one carries a recommended intake alongside an upper level, both stated in one consistent unit. Those documents are the tiebreaker when two sources disagree about how much is reasonable. They are also written in the units that the conversion, once you have done it, will land you in.
One limit worth naming: none of this tells you how well any of it absorbs. Unit conversion tells you what is in the serving. What reaches circulation is a different question, shaped by the form, the matrix and your own digestion, and no label arithmetic answers it.
So the sequence runs like this. Read the standardised marker line. Convert both products to milligrams. Confirm the serving count. Then look at what a day costs. The number that survives those four steps is the one worth acting on.
Frequently asked questions
What is the difference between mg and mcg?Show answerHide answer
A microgram is a thousandth of a milligram, so the number looks much larger.
Why do some labels use IU?Show answerHide answer
Older units like IU describe biological activity rather than weight.
How do I compare across units?Show answerHide answer
Convert to the same unit first, then compare per serving.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
