Peptide Reconstitution Calculator

Enter what is in the vial, how much bacteriostatic water you are adding, and the dose you have been given. This works out the concentration, the exact reading on a U-100 insulin syringe, how many doses the vial holds and how long it lasts. It does not recommend a dose — that number has to come from a prescriber.

Draw to 5 units 0.05 mL on a 1 mL (100 units) syringe

5mg per mL

50mcg in one unit

40whole doses in the vial

40days the vial lasts

1.75mg per week

35units per week

The vial holds 40 whole doses, but at this frequency only 28 fall inside a 28-day window — 12 would be discarded unused.

In plain words

The same answer without the jargon. Every line below updates as you change the numbers above.

1
Your bottle holds 10 mg of dry powder.
2
You mixed it with 2 mL of bacteriostatic water.
3
So the liquid is 5 mg in every 1 mL. One unit on the syringe holds 50 mcg.
4
For your 250 mcg dose you need 0.05 mL of the liquid — which is 5 units on a U-100 insulin syringe. Not 0.05 units, and not 5 mL. Units and millilitres are different things.
5
The bottle contains 40 whole doses (10 mg ÷ 0.25 mg per dose). At 7 a week that is 40 days of doses.
6
The real-world limit. Once mixed, if you discard the vial after 28 days you would use 28 of those 40 doses and throw the rest away. How long a mixed vial keeps is set by the product's label, not by this arithmetic. Many multi-dose products state a window measured in weeks. A compound with no approval has no established figure at all — nobody has run the stability or sterility work that would produce one.

Your summary

The three mistakes people actually make

Reading units as millilitres. On a U-100 syringe one unit is 0.01 mL. Drawing to "0.2" on a unit scale when you meant 0.2 mL gives you a fiftieth of the dose; the reverse gives you fifty times it.
Thinking more water means a weaker dose. It does not. The bottle holds the same milligrams whatever you dissolve them in. More water simply means you draw more units to get the same amount.
Planning around the arithmetic instead of the label. The maths will happily tell you a vial holds forty doses. Whether the liquid is still fit to use by then is a completely separate question, and the answer is on the product's label if it has one.

The same vial and dose, at four diluent volumes

This is the comparison people actually want: what changes if you use 1 mL instead of 2. The dose is identical in every row. Only the reading on the syringe moves.

Water added	Concentration	One unit holds	Your dose is
1 mL	10 mg/mL	100 mcg	2.5 units
2 mL	5 mg/mL	50 mcg	5 units
3 mL	3.3333 mg/mL	33.33 mcg	7.5 units
5 mL	2 mg/mL	20 mcg	12.5 units

Chart showing that the number of syringe units for a fixed dose rises in proportion to the bacteriostatic water added to a 10 mg vial. — The relationship is linear: double the diluent, double the units for the same dose.

What reconstitution actually changes

Three-step diagram: drawing bacteriostatic water, adding it to a vial of lyophilised peptide, and the resulting solution of known concentration.

A lyophilised vial holds a fixed mass of peptide as a dry cake. Adding bacteriostatic water dissolves it and creates a solution of known strength. The mass in the vial never changes. What the diluent volume decides is the concentration, and therefore how far along the syringe barrel a given dose sits.

That is why the choice of 1 mL versus 2 mL is not a question about potency. It is a question about whether the dose you need lands somewhere you can read accurately. A dose that works out to 1.2 units on a syringe graduated every 2 units cannot be measured; the same dose at half the concentration is 2.4 units, which still cannot be read precisely, and at a quarter it is 4.8 units, which can.

The number that goes wrong: units are not millilitres

A U-100 insulin syringe drawn with graduations every two units, showing that 100 units equals one millilitre.

On a U-100 syringe, one unit is one hundredth of a millilitre. A calculation that produces "0.25 mL" and a syringe reading of "25 units" describe the same volume. Reading one as the other is a hundred-fold error in whichever direction it is made, and it is not a hypothetical: regulators have attributed reported overdoses of self-measured injectable products to people drawing to a millilitre figure on a unit scale.

The safeguard is to work in one currency and check the other. If the calculator says 5 units, that is 0.05 mL, which is a twentieth of a 1 mL syringe — a short draw near the bottom of the barrel. If that does not match what you are looking at, the arithmetic and the syringe disagree, and the arithmetic is not the thing to trust blindly.

The arithmetic, if you want to check it

Concentration is the vial amount divided by the diluent volume. Dose volume is the dose divided by that concentration. Units are that volume multiplied by one hundred. Doses per vial is the vial amount divided by the dose, rounded down, because a partial dose left at the bottom is not a dose.

Worked through with the defaults on this page: 10 mg into 2 mL is 5 mg/mL. A 250 microgram dose is 0.25 mg, and 0.25 divided by 5 is 0.05 mL. Multiplied by one hundred that is 5 units. The vial holds 10 divided by 0.25, which is 40 whole doses, and at seven a week that is a little under six weeks — assuming the solution is still sound that long, which is a separate question the arithmetic cannot answer.

What this calculator cannot tell you

It cannot tell you what dose is appropriate, and it does not try. It has no per-compound presets for that reason: a suggested dose for a compound that has never completed a human trial is not a calculation, it is an invention. Many of the peptides people reconstitute are not approved for human use in any country, and for those there is no established human dose to look up.

It also knows nothing about sterility, about how long a reconstituted vial remains usable, about whether the vial contains what the label claims, or about how much of the labelled mass is peptide rather than counterion and water. Those are the questions that decide whether the number on the syringe means anything, and they are covered elsewhere on this site.

The two vials

Illustration of a sealed glass vial containing a lyophilised peptide cake labelled 10 mg. — **Peptide vial.** A fixed mass of dry powder. The milligram figure on the label is what the arithmetic starts from — though how much of that mass is peptide rather than salt and water is its own question.

Illustration of a glass vial of bacteriostatic water containing 0.9 percent benzyl alcohol, used as a diluent. — **Bacteriostatic water.** Water with roughly 0.9% benzyl alcohol, which inhibits bacterial growth and is what permits more than one entry into a vial. Not interchangeable with sterile water, which has no preservative.

Common questions

If I put 1 mL of bacteriostatic water into a 10 mg vial, how many units is one dose?

One millilitre into a 10 mg vial gives 10 mg per millilitre. On a U-100 syringe one unit is 0.01 mL, so one unit holds 0.1 mg, which is 100 micrograms. A 250 microgram dose is therefore 2.5 units. With 2 mL of water the same vial becomes 5 mg per millilitre, one unit holds 50 micrograms, and the same 250 microgram dose is 5 units. The amount of peptide is identical in both cases — only the volume it is dissolved in changed.

Does adding more water make the dose weaker?

No. It makes the solution more dilute, which means you draw more units to get the same dose. The vial still contains exactly what it contained. This is the most common misunderstanding about reconstitution, and it matters because it works in the opposite direction to intuition: more water means more units on the syringe, not less drug per dose.

What is the difference between a unit and a millilitre?

A millilitre is a volume. A unit is a graduation on an insulin syringe. On a U-100 syringe, the type these calculations assume, one unit is one hundredth of a millilitre, so 100 units fill 1 mL. Reading a figure in millilitres as though it were units, or the reverse, is a hundred-fold error. Regulators have attributed reported overdoses of self-measured products to exactly this confusion.

How many doses will one vial give me?

Divide the vial amount by the dose, using the same unit for both. A 10 mg vial at a 250 microgram dose is 10 divided by 0.25, which is 40 whole doses. The volume of diluent does not change that number. It changes how much you draw each time, not how many times you can draw. The calculator also shows how long that lasts at the frequency you enter.

How much bacteriostatic water should I use?

That is a measurability question rather than a correctness question. Any volume gives a valid concentration, so the practical range is the one where your dose lands somewhere readable on your syringe — not so small that it sits under the first graduation, and not so large that it exceeds the barrel. The calculator flags both ends. The vial also has a physical capacity that the arithmetic knows nothing about.

Does this calculator tell me what dose to take?

No, and it never will. It converts a dose you already have into a concentration and a syringe reading. What dose is appropriate, whether a compound should be used at all, and whether it is lawful to obtain are separate questions that belong with a qualified prescriber who knows your history. Many compounds people reconstitute have never been approved for human use anywhere.

Is bacteriostatic water the same as sterile water?

They are not interchangeable. Bacteriostatic water contains benzyl alcohol at around 0.9 percent, which inhibits bacterial growth and is what allows a vial to be entered more than once. Sterile water has no preservative and is intended for single use. Benzyl alcohol is also the reason bacteriostatic water is contraindicated in neonates and is generally avoided in pregnancy.

This is an arithmetic tool, not medical advice. It converts a dose you supply into a syringe reading and nothing more. It does not tell you what to take, whether to take it, or whether obtaining it is lawful where you are. Many compounds people reconstitute have never been approved for human use anywhere. Speak to a qualified healthcare professional who knows your history, and never rely on a number from a web page for something you are about to inject.