Reconstitution sounds technical, but it is a simple idea with a precise procedure: you take a vial of freeze-dried powder, add a measured amount of liquid, and end up with a solution of known strength. Everything after that is arithmetic — and this guide covers both halves, the handling and the maths, because getting either one wrong ruins the other.
Try the calculator with your own vial size and water volume.
What reconstitution means.
Peptides are usually supplied as a lyophilised powder — freeze-dried solid sitting at the bottom of a sealed vial. In that state you cannot measure a dose at all. Reconstitution is simply dissolving that powder in a measured volume of liquid, normally bacteriostatic (BAC) water, so the vial contains a solution of a known strength. Once you know how much peptide is in the vial and how much water you added, you know exactly how much peptide is in every millilitre — and therefore in every syringe unit.
The liquid: bacteriostatic water.
The standard diluent is bacteriostatic water (BAC water): sterile water for injection containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol stops bacteria growing between uses, once the vial has been punctured — which is why BAC water is the usual choice for a vial you will draw from more than once. Plain sterile water has no preservative; sources report it only when a specific peptide is documented as incompatible with benzyl alcohol, and a vial mixed with sterile water alone keeps for a much shorter time (around 24 hours). BAC water containing benzyl alcohol should not be used in newborns. Unopened BAC water does not need refrigeration until it is opened; once opened, keep it in the fridge.
What you need.
Your lyophilised peptide vial, a BAC water vial, a sterile syringe and needle for the transfer, alcohol swabs (70% isopropyl alcohol), a clean flat work surface, good light, and a pen to label the vial.
The steps.
- Wash your hands and clean the surface. Soap and water — one source specifies at least 20 seconds — then dry with a clean paper towel. Wipe the work surface with disinfectant or 70% isopropyl alcohol and let it air-dry. Some sources suggest nitrile gloves as an extra barrier; they are presented as optional, not required.
- Inspect the vial. Look through the glass before you mix anything. A healthy powder cake is normally white or off-white, a solid plug or loose powder — both are normal. Do not use the vial if you see discoloration (yellow or brown), moisture, visible specks, a melted or syrupy look, a shrunken or cracked cake, a cloudy film, a cracked vial, or a damaged stopper. Check the label and the expiry date, and make sure the vial is the one you intended. If the vial was refrigerated, some sources suggest letting it sit 15–20 minutes to reach room temperature first, because cold glass can draw in moisture — that figure comes from two sources only, so treat it as a suggestion rather than a rule.
- Swab both stoppers — and let them dry. Take the flip caps off. Wipe the rubber stopper of both vials firmly with a fresh alcohol swab, in a circular motion from the centre outward. Then wait: the stopper must air-dry completely before you puncture it. Do not blow on it or fan it — breath carries bacteria, and a needle pushed through wet alcohol can carry alcohol into the solution. Sources disagree on the drying time (10 seconds, 15–30 seconds, about 30 seconds), so the practical rule is simple: wait until it looks and feels dry. Use a fresh swab per stopper, and do not touch a swabbed stopper or an uncapped needle afterwards.
- Decide the water volume first — then draw it. The volume of water you add fixes the concentration for the life of that vial, so decide it before you draw anything. Adding more later invalidates every calculation you already made, and water cannot be removed. Typical volumes in sources are 1, 2 or 3 mL — a reported range, not a recommendation for any specific vial. To draw: inject air into the BAC water vial first (it equalises the pressure and makes drawing easier), invert the vial, and slowly draw the chosen volume with the needle tip below the liquid line. Tap the barrel to float bubbles to the top and push them back, then check the volume against your calculation before the needle goes anywhere near the peptide vial.
- Inject the water slowly down the vial wall — never straight onto the powder. Put the needle through the peptide vial’s stopper at a slight angle, with the vial tilted about 45° and the bevel toward the wall. Press the plunger slowly and steadily, letting the water trickle down the glass and pool at the bottom around the powder. Sources call this the single most important physical-handling step: a direct, fast stream can shear and damage the fragile peptide chains.
- Dissolve gently: swirl, never shake. Take the needle out and let the vial sit still for 30–60 seconds — many peptides start dissolving on their own. Then swirl gently in slow circles, or roll the vial between your palms, until it is dissolved. Never shake. Shaking makes foam and bubbles and shear forces that can unfold (denature) the peptide chains. How long dissolving takes varies by source — seconds, 30–60 seconds, 60–90 seconds of gentle swirling, up to a few minutes — so do not treat any one figure as a rule. If powder remains, let it sit and swirl again; do not warm it or shake it to force the issue.
- Look at the finished solution. A properly mixed solution should be clear and colourless (a very faint colour or slight opalescence is acceptable for some peptides). Cloudiness, visible particles after 30 minutes or more, persistent lumps, or discolouration mean the solution is compromised — sources say do not use it. (The “clear” rule is qualified in sources with “for some peptides” — a blue tint, for example, is normal for GHK-Cu.)
- Label it, then refrigerate immediately. Write on the vial: peptide name, concentration, reconstitution date and discard date. Put the used transfer needle in a sharps container, not back in its cap.
The three numbers you need.
Every calculation on this site comes down to three figures:
- Vial size (mg) — printed on the vial label. This is the total powder in the vial, not the dose.
- Water added (mL) — the volume of BAC water you put in. You choose this, so write it down.
- Your dose (mcg or mg) — given to you by your prescriber or provider. This guide never suggests one.
The formula.
Concentration (mcg/mL) = (vial mg × 1,000) ÷ water mL. Syringe units = (dose mcg ÷ concentration) × 100.
Worked example 1 — a 5 mg vial in 2 mL.
Concentration: (5 × 1,000) ÷ 2 = 2,500 mcg/mL. Each syringe unit (0.01 mL) therefore contains 2,500 ÷ 100 = 25 mcg. An example dose of 250 mcg needs 250 ÷ 25 = 10 units (0.1 mL). Doses per vial: 5,000 ÷ 250 = 20 doses.
Worked example 2 — a 10 mg vial in 3 mL.
Concentration: (10 × 1,000) ÷ 3 = 3,333 mcg/mL. Each unit contains 3,333 ÷ 100 = 33.3 mcg. An example dose of 500 mcg needs 500 ÷ 33.3 = 15 units (0.15 mL). Doses per vial: 10,000 ÷ 500 = 20 doses.
Choosing how much water — the maths trade-off.
The water volume does not change how much peptide is in the vial; it only changes how concentrated the solution is, and that is purely a measurement question. Less water means a higher concentration and fewer units per dose — but small draws are harder to measure precisely, and a one-unit reading error is a bigger fraction of the dose. More water means a lower concentration and more units per dose — the draw is larger and easier to read accurately. Whichever volume you use, write it on the vial or its box: unit numbers from a previous mix are wrong for a new one.
Check your answer backwards.
A quick reverse check catches most errors: take your answer in units, divide by 100 to get mL, and multiply by the concentration. You should get your dose back. Example: 10 units ÷ 100 = 0.1 mL, × 2,500 mcg/mL = 250 mcg — the dose you started with. If the reverse check does not return your dose, something is wrong; recalculate or ask a pharmacist.
Storage.
Before mixing, lyophilised peptides are typically kept at −20 °C for long-term storage, or 2–8 °C for shorter periods (exact figures vary by peptide). After mixing, refrigerate at 2–8 °C (36–46 °F) immediately, store upright and away from direct light, and do not freeze a reconstituted vial — freezing and freeze–thaw cycles form ice crystals that can damage the peptide. At room temperature a mixed vial degrades much faster (one source gives 24–48 hours maximum — a maximum, not a recommendation). How long a mixed vial is said to keep is the least settled figure on this site: most sources cite around 28 days refrigerated with BAC water, while others say 4–6 weeks. Treat 28 days as the commonly cited planning window, note that sources vary, and follow your product’s own label if it gives a shorter window.
Common reconstitution mistakes.
Shaking the vial. Spraying water directly onto the powder. Not swabbing the stoppers, or puncturing through wet alcohol. Deciding the water volume after the powder is already wet. No preparation-date label, so the vial’s age cannot be tracked. Freezing a mixed vial, leaving it at room temperature, or exposing it to light. Using the dose from a protocol instead of the milligrams printed on your vial. Reading the vial size in mg but entering a dose in mcg without converting.
FAQs
Does reconstitution change how much peptide is in the vial?
No. The powder amount is fixed by the label. Adding water only spreads that same amount through a larger or smaller volume, which changes the concentration — and therefore how many units make up a dose.
Can I use the calculator for any peptide?
Yes. The formula depends only on milligrams, millilitres and micrograms, so it is identical for every vial. The per-peptide pages simply pre-set the common vial sizes.
What if my dose comes out above 100 units?
That is a red flag. A single draw larger than a full 1 mL syringe usually means a unit mix-up — most often mg read as mcg. Stop, recheck the vial label and the dose units, and confirm with your provider or pharmacist.
How long does a reconstituted vial last?
That is a storage question, not a maths question, and the honest answer is that sources disagree: around 28 days refrigerated with BAC water is the most commonly cited figure, with some sources saying 4–6 weeks. Follow the instructions supplied with your vial and ask your pharmacist — this site does not give storage or usage guidance beyond reporting what sources commonly cite.
Educational reference only — not medical advice. This guide describes maths and commonly reported handling steps only; it does not recommend any dose. Always confirm your dose and preparation with a licensed healthcare provider or pharmacist.