How do you calculate peptide concentration after reconstitution?

Divide the amount of peptide in the vial by the volume of bacteriostatic water you add. For example, 10 mg of peptide reconstituted with 2 mL of water gives 5 mg/mL, or 5000 mcg/mL. The concentration is fixed once the water is added; drawing a smaller or larger volume changes the amount, not the concentration.

How much bacteriostatic water should I add to a peptide vial?

There is no single correct amount — it is a research choice that sets your concentration. More water gives a lower concentration and a larger, easier-to-measure draw volume; less water gives a higher concentration in a smaller volume. Common choices are 1 mL, 2 mL or 3 mL per vial. Use the calculator on this page to see what each option produces.

What is bacteriostatic water used for in reconstitution?

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol, which suppresses bacterial growth so a reconstituted vial stays stable in the fridge for longer than plain sterile water would allow. It is the standard diluent referenced in peptide reconstitution for research.

Peptide Reconstitution Calculator

Reconstitution is where a lyophilised (freeze-dried) research peptide is dissolved in a diluent so it can be measured accurately. The one number that matters is concentration — how much peptide sits in each millilitre of solution — because that's what lets a researcher work in consistent, documented units. This calculator does the arithmetic; the notes below explain exactly what it's doing so you can check it yourself.

Work it out

Peptide in the vial (mg)

Bacteriostatic water added (mL)

Amount you want to draw (mcg) — optional

How the maths works

The concentration is simply the peptide amount divided by the water added:

Concentration (mg/mL) = peptide (mg) ÷ water (mL)
Multiply by 1000 to express it in mcg/mL, which is usually the more convenient unit.

So a 10 mg vial reconstituted with 2 mL of bacteriostatic water gives 5 mg/mL, i.e. 5000 mcg/mL. That concentration is now fixed — it doesn't change no matter how much you draw. Drawing a smaller volume simply gives you a smaller amount at the same concentration.

Turning a target amount into a volume

To find the volume that contains a given amount:

Volume to draw (mL) = target amount (mcg) ÷ concentration (mcg/mL)

Using the example above (5000 mcg/mL): a 250 mcg target is 250 ÷ 5000 = 0.05 mL. On a standard 1 mL insulin-style syringe marked in 100 units, that's 5 units. The calculator returns both the millilitre volume and the unit mark so the reading is unambiguous.

More water or less water?

How much diluent to add is a research choice, not a fixed rule, and it's a trade-off:

More water → lower concentration → a larger draw volume for the same amount, which is easier to measure precisely.
Less water → higher concentration → a smaller draw volume, useful when a vial needs to last but harder to measure at fine increments.

Many researchers settle on 1–3 mL per vial so the common draw volumes land on clean, readable syringe marks. Change the water figure in the calculator to see how each option shifts the numbers.

Handling notes

Reconstituted peptides are generally kept refrigerated and protected from light; the benzyl alcohol in bacteriostatic water is what lets a mixed vial stay usable for longer than plain sterile water would allow. For the full storage picture, see our guide on storing and reconstituting peptides.

Sourcing documented material

Accurate reconstitution maths only means something if the vial actually contains what the label says. Every batch we hold is independently tested with a published Certificate of Analysis stating purity and identity — you can see the actual lab results in the CoA Library before you buy.

Shop batch-tested research peptides

This calculator and article are provided for laboratory and in-vitro research reference only. All products are supplied strictly for research use — not for human or veterinary consumption. This is not medical advice or dosing guidance for use in humans.