How do I calculate retatrutide dose in syringe units?

Divide your target dose (mg) by the concentration (mg/mL), then multiply by 100 to convert to units on a U-100 insulin syringe. For example, 4 mg at 10 mg/mL concentration equals 0.4 mL, or 40 units.

What concentration should I reconstitute retatrutide to?

A common research setup is 10 mg/mL (10 mg vial with 1 mL bacteriostatic water). This puts typical research doses on round syringe marks. Use the calculator to test different water volumes.

How much bacteriostatic water for a 10 mg retatrutide vial?

For 10 mg/mL concentration, add 1 mL of bacteriostatic water to a 10 mg vial. For 5 mg/mL, add 2 mL. The calculator shows the exact units for any combination.

Retatrutide Dosage Calculator: Reconstitution & Unit Math

By PeptCalc — Medically reviewed by David Mansour, MD — Last reviewed July 8, 2026

Retatrutide is supplied as lyophilized powder that must be reconstituted before use. This calculator reference explains how to convert a retatrutide vial and target dose into the exact number of units to draw on a U-100 insulin syringe. It is written for research purposes only and is not medical advice.

What the calculator does

The retatrutide dosage calculator handles the reconstitution math in two directions:

Forward mode — you enter vial size, water volume, and target dose → it returns the syringe units to draw.
Reverse mode — you enter vial size, target dose, and desired syringe units → it tells you how much water to add.

Both modes work from the same underlying formula: concentration equals mass divided by volume, and dose in units equals dose in volume times 100 (on a U-100 syringe).

Common retatrutide vial sizes

Research vials are typically supplied in:

10 mg
15 mg
20 mg
30 mg

The calculator supports any vial size. These are the most frequently seen.

Typical research concentration

A standard reconstitution setup for retatrutide is 10 mg/mL — meaning a 10 mg vial is reconstituted with 1 mL of bacteriostatic water. This concentration places commonly-cited research doses on round unit marks:

Target dose	Units at 10 mg/mL
1 mg	10 units
2 mg	20 units
4 mg	40 units
8 mg	80 units

Lower concentrations (more water) give larger, easier-to-measure draws but use up vial space faster. Higher concentrations (less water) mean smaller draws. The calculator lets you test any combination to find what works.

The math

Step 1: Calculate concentration

Concentration = vial mass ÷ water volume

10 mg vial + 1 mL water = 10 mg/mL
20 mg vial + 2 mL water = 10 mg/mL
10 mg vial + 2 mL water = 5 mg/mL

Step 2: Convert dose to volume

Volume (mL) = dose (mg) ÷ concentration (mg/mL)

Example: 4 mg dose at 10 mg/mL concentration = 4 ÷ 10 = 0.4 mL

Step 3: Convert volume to syringe units

On a U-100 insulin syringe, 1 mL = 100 units, so:

Units = volume (mL) × 100

Example: 0.4 mL × 100 = 40 units

The calculator performs these three steps instantly for any vial/dose/water combination you enter.

Reconstitution process

Gather supplies — peptide vial, bacteriostatic water, U-100 insulin syringes, alcohol swabs.
Swab both vial stoppers with alcohol.
Draw the calculated water volume (e.g. 1 mL for 10 mg/mL).
Inject slowly down the inside wall of the peptide vial, not directly onto the powder.
Swirl gently — do not shake. Let it dissolve completely.
Verify the concentration matches what you entered in the calculator.

For a detailed walkthrough, see How to Reconstitute Peptides.

Storage

Reconstituted peptide vials are generally stored refrigerated and protected from light. Unreconstituted lyophilized powder is stable at room temperature until the expiration date on the vial. Track the reconstitution date.

Why concentration matters

The same dose can be drawn at different unit marks depending on how much water you add:

4 mg dose from a 20 mg vial:

Water added	Concentration	Draw volume
2 mL	10 mg/mL	40 units
4 mL	5 mg/mL	80 units

Neither is "wrong" — the math is identical. The calculator shows both options so you can choose the draw size that's easiest to measure accurately on your syringe.

Common mistakes

Confusing mg and mcg. Retatrutide doses are in milligrams (mg), not micrograms (mcg). 1 mg = 1000 mcg. Double-check your units before drawing.
Shaking the vial. Swirl gently instead — shaking can denature the peptide.
Forgetting which concentration you used. If you reconstitute multiple vials at different concentrations, label each one. Drawing the wrong units from the wrong concentration is the most common dosing error.
Using a non-U-100 syringe. The calculator assumes a standard U-100 insulin syringe (100 units = 1 mL). If your syringe is marked differently, the unit conversion will not match.

Use the calculator

Enter your retatrutide vial size, bacteriostatic water volume, and target dose into the retatrutide calculator to see the exact syringe units. The reverse mode also works — put in your target dose and the units you want to draw, and it tells you how much water to add.

The calculator handles the math. This guide explains what the numbers mean and where they come from.