Peptide Reconstitution Calculator

Peptide reconstitution calculator: type your peptide vial size and the bac water you add, and see the concentration in mg/mL. It does the math only and never gives a dose.

Last updated October 4, 2026

Result

peptidereconstitutioncalculator.app, printed

Enter a peptide vial size and the bac water you add to see the concentration.

The formula

Concentration = mass ÷ volume

Worked example: a peptide vial holds 10 mg and 2 mL of bac water is added. 10 mg in 2 mL of bac water = 5 mg/mL. One mg is 1,000 mcg, so that is also 5,000 mcg/mL.

What concentration means

Concentration tells you how much powder sits in each mL of liquid. It is written as mg/mL, which you say as "milligrams per milliliter."

When you add liquid to a vial of dry powder, the powder dissolves. The amount of powder stays the same, and the liquid just spreads it out. More liquid means each mL holds less, and less liquid means each mL holds more.

The calculator takes the two numbers you type and divides one by the other. That is the whole job.

How the math works

The formula is short:

Concentration = mass divided by volume

Here is how to work it out by hand.

Find the mass on the vial label. Say it reads 10 mg.
Find the total liquid you added. Say it is 2 mL.
Divide the mass by the liquid. 10 divided by 2 is 5.
Your answer is 5 mg/mL.
To get mcg/mL, times it by 1,000. That gives 5,000 mcg/mL.

The calculator does this same math with your own numbers. It shows the concentration in mg/mL and mcg/mL only. You can print the result card.

More worked examples

These use round numbers so you can check them in your head.

Peptide vial size	Bac water added	Concentration	Same, in mcg/mL
5 mg	1 mL	5 mg/mL	5,000 mcg/mL
5 mg	2 mL	2.5 mg/mL	2,500 mcg/mL
10 mg	1 mL	10 mg/mL	10,000 mcg/mL
10 mg	4 mL	2.5 mg/mL	2,500 mcg/mL
20 mg	2 mL	10 mg/mL	10,000 mcg/mL
20 mg	5 mL	4 mg/mL	4,000 mcg/mL

Look at the 5 mg rows: doubling the liquid cuts the concentration in half, while the mass in the vial stays the same.

Find the liquid for a target concentration

Sometimes you know the concentration you want and need the volume. The helper below does it for you, or flip the formula by hand:

Volume = mass divided by concentration

Say a vial holds 10 mg and you want 2 mg/mL. 10 divided by 2 is 5. So the total liquid would be 5 mL.

Say a vial holds 6 mg and you want 3 mg/mL. 6 divided by 3 is 2. So the total liquid would be 2 mL.

Water for a target concentration

Math only. It does not give a dose or say how much to use.

Bac water to add enter both numbers

This is only math. The right liquid and the right volume come from the product's own label, or from your clinician or pharmacist. Also check that the vial can hold that much liquid.

How mg and mcg relate

One milligram (mg) is 1,000 micrograms (mcg). So:

To turn mg into mcg, times by 1,000. 2 mg is 2,000 mcg.
To turn mcg into mg, divide by 1,000. 500 mcg is 0.5 mg.

Labels may use either unit. The calculator takes the peptide vial size in mg or mcg. Pick the one that matches your label.

How U-100 syringe units work

A U-100 syringe is marked in units, not mL. On it, 100 units fill 1 mL, so one unit is 0.01 mL. To get mL, divide the units by 100. So 20 units is 0.2 mL, and 0.3 mL is 30 units. This scale comes from the FDA label for a U-100 insulin, listed in the sources below.

U-100 syringe: units to mL

Volume conversion only. It does not tell you how much to use. Other syringe types (U-40, U-500) use different scales.

Syringe size

0.3 mL (30 units) 0.5 mL (50 units) 1 mL (100 units)

Same volume enter units or mL

Type units or mL to see it on the syringe.

The syringe size, such as 0.3 mL, 0.5 mL or 1 mL, only changes how far the marks go. The converter turns volume into units and back. It does not say how much to use.

Concentration chart

Want to see many results at once? The peptide reconstitution chart shows a grid of vial sizes and liquid volumes. Each cell is the mg/mL you get. It is made by the same formula as this calculator, so the two always agree. It has no doses and no product names.

What liquid is used to reconstitute?

The liquid is often bacteriostatic water. That is sterile water with benzyl alcohol, a preservative that slows germ growth. Read more in what is bacteriostatic water.

Some products need plain sterile water instead. The bacteriostatic water label says to follow the drug maker's own instructions for which liquid to use. See bacteriostatic water vs sterile water for the difference.

Once a multi-dose vial of water is opened, CDC guidance says to date it and throw it out within 28 days, unless the maker says otherwise. Dating is easy to skip: in one hospital survey, only half of the opened vials had a date on them (Mattner and Gastmeier, 2004).

How to reconstitute a vial

Clean your hands and your work surface.
Add the liquid the product label names. Its own instructions decide how to mix it.
Let the powder dissolve, then label the vial with the date and the concentration.

The full walkthrough is in how to reconstitute peptides.

What this calculator does not do

It does not give a dose or say how much to take.
It does not turn amounts into syringe units to draw.
It does not name any product or give mixing recipes.
It does not store what you type. The math runs in your browser.

It is for education only. It is not medical advice. For anything about your own use, ask a clinician or pharmacist.

Frequently asked questions

How do you calculate peptide reconstitution?

Divide the mass in the vial by the total liquid you add. For example, 10 mg in 2 mL is 5 mg/mL. The answer is the concentration.

How do you calculate concentration?

Take the mg on the vial label and divide it by the mL of liquid in the vial. The result is the concentration in mg/mL.

What is mg/mL?

mg/mL means milligrams per milliliter. It tells you how much of the powder is in each mL of liquid. So 5 mg/mL means each mL holds 5 mg.

How many mL is 10 units on a U-100 syringe?

10 units on a U-100 syringe is 0.1 mL, because 100 units fill 1 mL. That makes one unit 0.01 mL. This site never converts a drug amount into units to draw.

How do I convert mg to mcg?

Times the mg by 1,000. So 1 mg is 1,000 mcg, and 5 mg/mL is 5,000 mcg/mL. To go back, divide by 1,000.

What does reconstitute mean?

To reconstitute means to add a liquid to a dry powder so it turns back into a solution. Adding more liquid does not change the amount of powder in the vial. It only changes how much sits in each mL.

Sources

Bacteriostatic Water for Injection, USP, prescribing label, DailyMed, US National Library of Medicine, read 2026-10-04
Preventing Unsafe Injection Practices, CDC, read 2026-10-04
U-100 insulin prescribing information (syringe scale: 100 units per mL), FDA label, read 2026-10-04
Bacterial contamination of multiple-dose vials: a prevalence study (Mattner F, Gastmeier P. Am J Infect Control. 2004;32(1):12-16. doi: 10.1016/j.ajic.2003.06.004, PMID 14755229), peer-reviewed study, read 2026-10-04