Reconstitution Calculator

Retatrutide Reconstitution Calculator

Work out how to mix a retatrutide vial. Enter the vial size and how much bacteriostatic water you plan to add, and this tool returns the concentration, the volume to draw, the insulin syringe units, and how many doses the vial holds. It does the arithmetic only. It does not tell you what dose to take.

Want a projected weight-loss timeline from your own stats instead? That is a different question. Use the retatrutide weight loss calculator for the timeline. This page is only about mixing and measuring.

Vial and water inputs

The fields load with example values so you can see the math right away. These are a placeholder to demonstrate the arithmetic, not a recommended or starting dose. Type or drag your own numbers, including the exact amount of bacteriostatic water you mixed. Disclaimer: educational only, not medical advice.

Total peptide in vial

1 mg30 mg

Bacteriostatic water added

0.5 mL5 mL

Dose per injection

0.1 mg15 mg

Insulin syringe size

Reconstitution result

Concentration

5 mg/mL

5000 mcg/mL

Volume per dose

0.4 mL

400 microlitres

Insulin syringe units

40 units

Draw to about the 40-unit mark on a U-100 syringe

Doses per vial

5 doses

Approximate, assuming exact reconstitution

Units assume a U-100 insulin syringe where 1 unit equals 0.01 mL.⁴Always cross-check with your supplier's recommended reconstitution volume.

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How retatrutide reconstitution works

Retatrutide is a triple hormone-receptor agonist studied for obesity in a published Phase 2 trial.¹ It ships as a freeze-dried (lyophilized) powder, which has to be dissolved in liquid before any dose can be measured.⁵ Reconstitution is that mixing step: you add a known volume of bacteriostatic water to the vial,² which turns the powder into a solution at a known concentration. That concentration is what lets a dose be drawn accurately.

The arithmetic has three steps, and the calculator above runs all three as you type:

concentration (mg/mL) = vial mg / water mL

volume per dose (mL) = dose mg / concentration

insulin units = volume per dose mL x 100

The last step uses the U-100 insulin syringe conversion, where 1 unit equals 0.01 mL.⁴ The amount of water you add changes the concentration and the volume you draw, never the total milligrams of peptide in the vial.

Why 2 mL is the default

This calculator pre-fills 2 mL of bacteriostatic water, and there is a safety reason behind that number. 2 mL fits comfortably inside common research vial sizes, so it never asks you to add a volume the vial physically cannot hold. A calculator that suggested, say, 5 mL for a 3 mL vial would produce unit counts that look authoritative but describe a mix you could never make, and that is exactly how a small measurement turns into a large error.

2 mL also keeps most draws in a range a U-100 syringe reads well. The trade-off is that a higher-strength vial gets concentrated, so the draw gets smaller. A 20 mg vial in 2 mL is 10 mg/mL, so a 0.5 mg amount is only 5 units. When any draw lands under about 5 units, the calculator flags it and tells you to draw slowly, because that is where a misread of one or two units matters most. It never silently rounds a small draw away.

The bacteriostatic water field stays free entry on purpose. 2 mL is the default, but you should enter the exact volume you actually mixed, and the concentration, units, and dose count will follow from your real number.

How to reconstitute a retatrutide vial

Swab both stoppers. Wipe the rubber stopper of the peptide vial and the bacteriostatic water vial with an alcohol swab and let them dry.
Draw the water. Draw the bacteriostatic water volume the calculator shows, 2 mL by default, into a syringe.
Inject down the wall. Insert the needle at a slight angle so the water runs down the inside wall of the vial rather than directly onto the powder. This reduces foaming.
Swirl, do not shake. Inject the water slowly. Do not shake the vial. Swirl gently until the solution is clear.
Label the vial. Label the vial with the reconstitution date and the concentration in mg per mL.
Refrigerate. Refrigerate the reconstituted vial. Do not freeze it. Follow the supplier storage instructions.

Worked examples

The amounts below are round numbers chosen to keep the arithmetic easy to follow. They are illustrations of the math, not doses to take. Use the figures your own protocol source specifies. Disclaimer: this is educational only, individual protocols vary, and dose decisions belong with a licensed clinician.

Example A: 10 mg vial, 2 mL water

Math illustration, not a dose to take. The concentration is 10 / 2 = 5 mg/mL. A 2 mg amount gives 2 / 5 = 0.4 mL, which is 40 units on a U-100 syringe. The vial contains 10 / 2 = 5 illustrative draws.

Example B: 20 mg vial, 2 mL water

Math illustration, not a dose to take. The concentration is 20 / 2 = 10 mg/mL. A 0.5 mg amount gives 0.5 / 10 = 0.05 mL, which is 5 units on a U-100 syringe. The vial contains 20 / 0.5 = 40 illustrative draws.

Notice that the same 2 mL of water gives very different unit counts depending on the vial strength. That is why you enter your own vial size rather than copying a unit number from somewhere else.

Reading the insulin syringe

Reconstituted peptides are almost always drawn with a U-100 insulin syringe. The conversion is fixed:

1 unit = 0.01 mL

100 units = 1 mL = full 1 mL barrel

So a 0.4 mL draw is 40 units, and a 0.05 mL draw is 5 units. The calculator shows both the millilitre volume and the unit count, and it checks the volume against the 0.3 mL, 0.5 mL, or 1.0 mL barrel you select. Smaller barrels have finer graduations and are easier to read for small draws.

How the water volume changes the draw

The volume of bacteriostatic water you add does not change how much peptide is in the vial. It changes the concentration, and with it the volume you draw for a given amount. A 10 mg vial reconstituted with 1 mL is twice as concentrated as the same vial with 2 mL, so the draw is half the liquid volume for the same amount.

Less water (1 mL)

More concentrated. Useful for a higher-strength vial where the draw would otherwise be tiny. The same amount becomes a smaller liquid volume.

2 mL, the default

Fits the vial and balances readability against concentration. Where this tool starts.

More water (3 mL)

More diluted. Spreads a small amount over a larger, easier-to-read draw. Useful when a draw would otherwise land under a few units.

If you want the same concentration math without a compound preset, the general peptide reconstitution calculator handles any vial, and the beginner injection guide walks through the mixing and measuring steps in plain terms.

Frequently asked questions

How much BAC water do I add to a retatrutide vial?

There is no single correct volume, because the water changes the concentration and how readable the draw is, not the amount of peptide in the vial. This calculator defaults to 2 mL, which fits common research vial sizes and keeps the draw in a readable range on a U-100 syringe. Enter your own vial size above to see the concentration and units at 2 mL, then compare what 1 mL or 3 mL would give you.

How many units is a 2mg retatrutide dose?

It depends entirely on the concentration you mixed. As a worked example, a 10 mg vial reconstituted with 2 mL is 5 mg/mL, so a 2 mg amount is 0.4 mL, which is 40 units on a U-100 insulin syringe. That is arithmetic on the numbers you enter, not a recommended dose. Disclaimer: this is educational only, individual protocols vary, and dose decisions belong with a licensed clinician.

How many doses does a retatrutide vial make?

Divide the total peptide in the vial by your per-injection amount. The calculator shows this as doses per vial. As a worked example, a 10 mg vial at a 2 mg amount is 5 draws, and a 20 mg vial at 0.5 mg is 40 draws. This assumes exact reconstitution and is an estimate, not a guarantee of yield. Disclaimer: educational only.

Can I use more or less water than 2 mL?

Yes. The total milligrams of peptide are fixed at reconstitution, so adding more water lowers the concentration and makes the same amount a larger, easier draw, while adding less water concentrates it into a smaller draw. The peptide in the vial does not change either way. 2 mL is the default here because it fits the vial and reads well on a U-100 syringe, but you should enter what you actually mixed.

What is the difference between BAC water and sterile water?

Bacteriostatic water contains a small amount of benzyl alcohol as a preservative, which keeps a punctured, reconstituted vial usable for up to about 28 days when kept refrigerated, the common convention for benzyl-alcohol-preserved water. Plain sterile water has no preservative, so a vial mixed with it should be used within hours, not weeks. For that reason bacteriostatic water is the standard choice for a multi-dose peptide vial.

Does this calculator tell me what dose to take?

No. It converts numbers you already have into a concentration, an injection volume, insulin syringe units, and a count of doses per vial. It performs the arithmetic only. It does not diagnose, prescribe, or choose a dose for you. The amount you enter has to come from your own protocol source or a clinician who knows your history. For a projected weight-loss timeline from your own stats, use the separate retatrutide weight loss calculator instead.

This is harm reduction education, not medical advice

This calculator is for educational use. It converts numbers you already have into a volume and a syringe reading. It does not choose a dose. Peptide protocols vary between individuals and compounds. Always cross-check with your protocol source, supplier instructions, and where possible a qualified clinician.