Purity vs net content: two numbers on every report
By BioGenisys Research Team · 4 min read · Updated 2026-10-27
Purity and net content are the two numbers people most often mix up on a lab report. Purity is how clean the compound is. Net content is how much of it is in the vial. A vial can be 99% pure and still hold a little more or less than its label says, and that isn't a contradiction. The figures here are made-up examples.
The short version
- Purity is a percentage: how much of the sample is the right compound.
- Net content is in milligrams: how much compound is actually in the vial.
- A few percent above or below the label is normal. A big shortfall is worth asking about.
An everyday comparison
Think of a bag of coffee beans. Purity is how many of the beans are coffee rather than stones or husks. Net content is how much the coffee in the bag weighs. A bag can be pure coffee and still weigh a little over or under what the label says.
| Purity | Net content | |
|---|---|---|
| The question it answers | How much of the sample is the right compound? | How many milligrams of the compound are in the vial? |
| How it's usually measured | HPLC, a test that separates the sample into its ingredients | Compared against a known reference sample, often on the same HPLC instrument |
| How it's shown | A percentage, such as 99.4% | Milligrams, next to the label amount |
| What it doesn't tell you | How much is in the vial | What else is in the vial |
Reading net content against the label
Filling a vial with a few milligrams of powder can't be exact to the decimal, so the measured amount rarely matches the label perfectly. Using a vial labeled 10mg as the example:
| Example reading | Against the label | What it means |
|---|---|---|
| 10.0 mg | Right on the label | The vial holds what the label says. |
| 10.8 mg | About 8% over | Common. Vials are often filled slightly over so none come up short. |
| 9.6 mg | About 4% under | A small shortfall within normal filling variation. Worth noting in your records. |
| 8.0 mg | About 20% under | A real shortfall. Ask the supplier about it before relying on the label amount. |
A difference of a few percent either way is normal. A large shortfall is the one worth questioning.
Why the powder isn't 100% peptide
The powder in a vial is mostly peptide, but not entirely. It also holds a small amount of salt left over from manufacturing and a trace of water. Net content measures only the peptide, not the whole powder. That's one reason a vial can read slightly under its label while still being over 99% pure. Peptide salt forms explains where that salt comes from.
Copper peptides and blends
A peptide carrying a metal, such as GHK-Cu (a peptide holding a copper atom), may be reported as a total, with the peptide and the copper listed separately underneath. Blends list each compound's amount on its own line, each checked against its own label amount.
Reading the two numbers together
- High purity, amount near the label: the expected result.
- High purity, amount above the label: clean compound, and a little more of it than stated.
- High purity, amount well below the label: the compound is clean, but there's less of it in the vial.
- Lower purity, amount near the label: about the right amount of material, with more of something else mixed in.
- No net content on the report: the amount wasn't tested. Ask for it, or consider the label amount unconfirmed.
Our reports are on the Certificates of Analysis page. For the rest of a report, see How to read a peptide lab report.
For research use only. Not for human or veterinary use.