Educational guide
Peptide Reconstitution Calculator — Units, Draw & Doses - Peptide Dosages
Peptide Reconstitution Calculator Enter your vial strength, bacteriostatic water, and target dose — get the exact draw volume, the mark to hit on an insulin syringe, and how many doses your vial holds. Works for any lyophilised peptide, and updates live as you
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Peptide Reconstitution Calculator
Enter your vial strength, bacteriostatic water, and target dose — get the exact draw volume, the mark to hit on an insulin syringe, and how many doses your vial holds. Works for any lyophilised peptide, and updates live as you type.
Reconstituting a peptide comes down to three numbers you already have: how much peptide is in the vial (in milligrams), how much bacteriostatic water you add (in millilitres), and the dose you want to draw. This peptide reconstitution calculator turns those three inputs into the four numbers you actually need at the bench — the concentration, the exact volume to draw, the mark to stop at on an insulin syringe, and how many doses the vial holds. It updates live as you type, and it flags setups that don’t physically make sense.
The math is identical for every lyophilised (freeze-dried) peptide — BPC-157, TB-500, semaglutide, ipamorelin, GHK-Cu, retatrutide, and the rest. The compound changes the dose you choose; it never changes the arithmetic that converts that dose into syringe units. That’s why one calculator covers them all.
How peptide reconstitution works
A lyophilised peptide arrives as a dry powder or thin cake at the bottom of a sealed vial. To draw a measurable dose you first dissolve it in a liquid — almost always bacteriostatic water (sterile water with 0.9% benzyl alcohol, which lets the vial be used over several days). Once dissolved, the peptide is spread evenly through that liquid, so the concentration is simply the total peptide divided by the total water:
From the concentration, everything else follows. To get a specific dose you draw a specific volume, and on a U-100 insulin syringe that volume is read in units, where 100 units = 1 mL.
The math behind the calculator
Under the hood the tool runs four short calculations. You never have to do them by hand, but seeing them makes the outputs easy to trust and easy to sanity-check.
Concentration
vial mg ÷ BAC water mL → mg per mL
Draw volume
your dose (in mg) ÷ concentration → mL to pull
Syringe units
draw volume × 100 (U-100) → the mark to hit
Doses per vial
vial mg ÷ dose mg, rounded down
If your dose is written in micrograms (mcg), convert it to milligrams first by dividing by 1,000 — 250 mcg is 0.25 mg. The calculator does this automatically when you switch the unit toggle; the formulas above always work in milligrams.
A worked example
Say you have a 5 mg vial, you add 2 mL of bacteriostatic water, and your target dose is 250 mcg on a U-100 syringe.
Concentration: 5 mg ÷ 2 mL = 2.5 mg/mL
Dose in mg: 250 mcg = 0.25 mg
Draw volume: 0.25 mg ÷ 2.5 mg/mL = 0.1 mL
On the syringe: 0.1 mL × 100 = 10 units
Doses per vial: 5 mg ÷ 0.25 mg = 20 doses
So you’d fill the insulin syringe to the 10-unit mark for each 250 mcg dose, and the vial would last 20 draws. Change any input above the fold and watch every number move.
How much bacteriostatic water should you use?
There is no single “correct” amount — the water volume is a dial you control to make the draw easy to read. More water gives a lower concentration and therefore a larger, easier-to-measure draw for the same dose. Less water concentrates the peptide and shrinks the draw. The goal is a mark that lands comfortably on the syringe, roughly between 5 and 50 units.
1.0 mL
100 units
Full syringe — the practical maximum
0.5 mL
50 units
Ideal — easy, precise
0.25 mL
25 units
Ideal
0.1 mL
10 units
Fine
0.05 mL
5 units
Getting small — add more water if you can
0.02 mL
2 units
Too small to measure reliably
A practical constraint sits on top of this: the water has to physically fit the vial. Small peptide vials typically hold around 3 mL of usable space; larger ones (for example some NAD+ vials) hold 10 mL. If the calculator warns that your water volume “may not fit,” you’ve likely over-diluted for that vial size.
Reading the units on an insulin syringe
Insulin syringes are marked in units, not millilitres, and the standard is U-100: 100 units = 1 mL. That single conversion is why the calculator can hand you a unit mark directly. A less common U-40 syringe uses 40 units per mL, so the same volume reads as a different number of units — the tool has a toggle for that. Whatever you draw, you’re reading a volume; the peptide dose is baked into that volume by your concentration.
Common vial sizes and what they mean
Vials are labelled by the total amount of peptide inside, most often in milligrams. Higher-strength vials aren’t a “stronger dose” — they simply pack more total peptide, so at the same concentration they yield more doses.
2 mg
1.0 mg/mL
Low-dose peptides (e.g. AOD-9604)
5 mg
2.5 mg/mL
Very common single-peptide size
10 mg
5.0 mg/mL
The default for many research peptides
15–30 mg
7.5–15 mg/mL
Higher-dose or longer-supply vials
Mistakes the calculator quietly catches
Beyond the numbers, the tool watches for setups that are arithmetically valid but physically wrong, and shows a warning instead of a misleading answer:
Too much water for the vial — over about 10 mL rarely fits a standard vial.
A dose larger than the whole vial — usually a units mix-up (mcg vs mg).
A draw over one full syringe — more than 100 units won’t fit; split the dose or add less water.
A draw under ~2 units — too small to measure accurately; use less water to raise the mark.
Storage and handling, briefly
Reconstituted peptides are generally kept refrigerated and used within a window that depends on the compound and the diluent. Bacteriostatic water is chosen precisely because its preservative allows multi-day use of an opened vial. Handling, sterility, and shelf-life are their own topic — see the full reconstitution guide for the practical detail, and always follow qualified professional guidance for anything beyond a research context.
Want the numbers and the context for a specific compound? Ask OpenPeptide, the site’s research assistant — it runs this same math and pulls the documented dosing for whatever peptide you’re working with, with sources.
Frequently asked questions
Reconstitution is dissolving a freeze-dried (lyophilised) peptide powder in a liquid — usually bacteriostatic water — so it can be measured and drawn accurately. Once dissolved, the peptide is spread evenly through the liquid, so a known volume contains a known dose.
There is no fixed amount — you choose it to make the draw easy to read. More water lowers the concentration and gives a larger, easier-to-measure draw; less water shrinks it. Aim for a draw between about 5 and 50 units on a U-100 syringe. Most people use 1–3 mL for common small vials, and the water must physically fit the vial (small vials hold ~3 mL).
First work out the concentration (vial mg ÷ water mL). Then divide your dose in mg by that concentration to get the draw volume in mL, and multiply by 100 for a U-100 syringe. The calculator above does all of this live — just enter your vial strength, water, and dose.
A U-100 syringe is marked in units where 100 units = 1 mL. It's the standard insulin syringe and the reason a dose can be read directly as a unit mark. A less common U-40 syringe uses 40 units per mL, so the same volume reads as a different number — the calculator has a toggle for both.
Divide the total peptide in the vial (mg) by your dose (mg) and round down. A 5 mg vial dosed at 250 mcg (0.25 mg) yields 20 doses. The water you add doesn't change the number of doses — only the dose size does.
Yes, in two ways. Physically, more water than the vial holds (roughly over 10 mL for standard vials) won't fit. Practically, very high dilution makes each draw so small it's hard to measure — the calculator warns you when a draw drops below about 2 units.
A draw above 100 units won't fit in a single 1 mL U-100 syringe. Either split it across two draws, or reconstitute with less bacteriostatic water so the same dose lands at a lower unit mark. The calculator flags this automatically.
Divide by 1,000. 250 mcg = 0.25 mg; 1,000 mcg = 1 mg. The calculator converts automatically when you switch the dose-unit toggle, so you can enter the dose in whichever unit your protocol uses.
No. The reconstitution and syringe math is identical for every lyophilised peptide — BPC-157, TB-500, semaglutide, ipamorelin, retatrutide and the rest. The compound only changes the dose you choose; it never changes how that dose converts to syringe units.
They use different unit scales: U-100 is 100 units per mL, U-40 is 40 units per mL. The same volume of liquid reads as a larger number of units on a U-100 syringe. Always match the calculator's syringe setting to the syringe in your hand.
It depends on the compound and the diluent, but reconstituted peptides are generally refrigerated and used within a defined window. Bacteriostatic water is preferred because its preservative allows an opened vial to be used over several days. See the full reconstitution guide for handling and shelf-life detail.
Yes — it's completely free, runs entirely in your browser, requires no sign-up, and stores nothing. Enter your numbers and read the result instantly.
Concentration is how much peptide sits in each millilitre of liquid (mg/mL), and it's the bridge between your dose and your syringe mark. Two vials of the same strength can give totally different unit marks for the same dose if they were reconstituted with different amounts of water — because their concentrations differ.
It can be. A draw under about 2 units is hard to measure precisely, so small errors become large percentage errors. If the calculator shows a very small draw, reconstitute with less bacteriostatic water so the same dose lands at a higher, more readable unit mark.
They differ in preservative: bacteriostatic water contains 0.9% benzyl alcohol, which lets an opened vial be used over several days, whereas plain sterile water has no preservative and is intended for single use. The math in the calculator is the same either way; the choice affects how long a reconstituted vial can be used.
You need a target dose to get a syringe mark, but you can also work backwards: set a water volume and read off how many units a given dose lands at, then adjust the water until the mark is easy to hit. For documented per-compound dosing, ask the OpenPeptide assistant or open that peptide's protocol page.