Research Tools
Peptide Dosage Calculator
Work out exactly how far to draw the plunger. Enter your syringe, your vial, and how much bacteriostatic water you added — we'll show you the mark to fill to.
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Common syringes
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units
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Concentration
Peptide per unit
Volume to draw
for one dose
Doses per vial
at this dose
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Read the mark at the front edge of the black rubber stopper — not at the tip of the plunger rod. Units are volume markings, not a weight: on a 1 ml / 100 unit syringe one unit is 0.01 ml.
Step by step
How to reconstitute a peptide
Lyophilized (freeze-dried) peptide is a fragile powder. Reconstitution is simply adding a measured volume of bacteriostatic water to it — the care is in how you add it.
1. Bring everything to room temperature
Take the vial out of the fridge and let it sit for 20–30 minutes. Adding cold diluent to cold powder slows dissolution and encourages the powder to clump against the glass.
2. Work clean
Wash your hands, then wipe the rubber stopper on both the peptide vial and the bacteriostatic water vial with a fresh alcohol swab. Let them air-dry — don't fan or blow on them. Use a new sterile needle and syringe every single time you puncture a stopper.
3. Draw the diluent
Draw the exact volume of bacteriostatic water you entered in the calculator above. Choosing that number is a trade-off, not a fixed rule: less water gives a stronger solution and a very small, hard-to-measure draw; more water gives a weaker solution that is easier to measure accurately but fills the vial faster. A draw that lands somewhere between 10 and 50 units on your syringe is comfortable to read.
4. Add it slowly, down the glass
Angle the needle so the stream runs down the inside wall of the vial and let it trickle in under gentle pressure. Never fire the water directly into the powder cake — the force of the jet is one of the easiest ways to damage the peptide.
5. Do not shake
Swirl the vial gently, or simply set it down and wait. Most peptides dissolve on their own within a few minutes. Shaking creates foam and shear forces that break the peptide apart; if you see a persistent head of bubbles, you shook it.
6. Inspect before you use it
The finished solution should be completely clear and colourless with no floating particles, no cloudiness, and no undissolved specks. If it isn't, discard it. A little residual powder ring at the shoulder of the vial usually just needs another few minutes of standing.
7. Label the vial immediately
Write the peptide name, the concentration (the mg/ml figure from the calculator) and the date you reconstituted it directly on the vial. An unlabelled vial in a fridge is a dosing error waiting to happen.
Handling
Storage best practices
Before mixing — lyophilized powder
- Refrigerate at 2–8 °C for routine storage.
- For long-term storage, keep at −20 °C or colder. Prefer a manual-defrost freezer — the auto-defrost cycle in a frost-free unit swings the temperature repeatedly.
- Keep the vial in its box. Light degrades many peptides, and tryptophan- and cysteine-containing sequences are especially sensitive.
- Keep it dry. Let a vial come to room temperature before opening it, or condensation will form inside.
- In powder form, most peptides are stable for years frozen and many months refrigerated.
After mixing — reconstituted solution
- Refrigerate at 2–8 °C. Never freeze a reconstituted vial — freeze–thaw cycles are one of the fastest ways to destroy a peptide.
- Store it on a shelf toward the back, not in the fridge door, where the temperature swings every time the door opens.
- Typical working window is 2–4 weeks refrigerated, though this varies a lot by sequence. Shorter is always safer.
- Bacteriostatic water contains 0.9% benzyl alcohol, which is what makes repeat punctures acceptable. Plain sterile water has no preservative and should be treated as single use.
- Swab the stopper with alcohol before every draw and keep the vial upright.
- Minimise time on the bench. Take out what you need, then put it straight back.
Get it right
Mistakes to avoid
Almost every reconstitution problem comes from one of the following.
Confusing milligrams with micrograms
This is the single most common and most consequential error. 1 mg = 1000 mcg. A vial labelled 5 mg contains 5000 mcg. Getting this wrong by one decimal place is a ten-fold error.
Treating "units" as a dose
Units on an insulin syringe measure volume, not peptide. The same 10 units can be 50 mcg or 500 mcg depending on how much bacteriostatic water you added. A unit count copied from someone else's protocol is meaningless unless their vial and dilution match yours.
Assuming more water means more peptide
The vial contains a fixed amount of peptide. Adding 3 ml instead of 1 ml doesn't triple anything — it just makes each unit one third as strong, so you draw three times as far for the same dose.
Shaking the vial
Shaking generates shear forces and an air–liquid interface that unfold and aggregate the peptide. It may still look clear afterwards while having lost potency. Swirl, or wait.
Firing the diluent straight into the powder
Injecting fast and directly onto the cake does the same damage as shaking. Angle the needle so the water runs down the glass wall.
Mixing two peptides into one vial
It is tempting to combine two compounds to save a draw, but it creates three problems at once: the compounds may not be chemically compatible or share the same pH optimum, each one's stability in solution is now unknown, and the ratio between them is locked forever — you can no longer adjust one without adjusting the other. Keep every peptide in its own labelled vial and draw them separately.
Using the wrong diluent
Sterile water, saline and bacteriostatic water are not interchangeable. Only bacteriostatic water is preserved for repeat access. Some poorly soluble peptides need a specific diluent entirely — check before you assume water will do.
Freezing or over-storing the reconstituted vial
Once it's in solution it belongs in the fridge and it has a clock on it. Freezing it, leaving it on the bench, or stretching a vial out for months are all ways to end up quietly working with a degraded product.
Reading the plunger from the wrong edge
Read the graduation at the leading (front) face of the rubber stopper, at eye level. Reading the back edge of the stopper adds a consistent error to every dose you draw.
Skipping the label
Two clear vials in a fridge look identical. Name, concentration, date — every time, on the vial itself.
For research use only. This calculator and the guidance on this page are provided for laboratory reference. BioStacks products are not intended for human or veterinary use, and nothing here is medical advice. Always verify your own arithmetic against the vial label before use.