How the math works
concentration (mg/mL) = mg in the vial ÷ total solution (mL) volume to draw (mL) = dose (mg) ÷ concentration units (U-100) = volume (mL) × 100
Nothing in the formula is specific to retatrutide. Two vials of the same size give different answers if they hold different amounts of liquid, which is why a dose in "units" means nothing without the vial size and the volume. If your dose is in micrograms, divide by 1,000 first: 500 mcg is 0.5 mg.
How much bac water for a 10 mg vial?
Mathematically there's no right answer: the liquid added only sets the concentration. What changes is how many units each milligram takes up on the syringe:
- 1 mL: 10 mg/mL, so each 1 mg is 0.1 mL = 10 units
- 2 mL: 5 mg/mL, so each 1 mg is 0.2 mL = 20 units
- 3 mL: 3.33 mg/mL, so each 1 mg is 0.3 mL = 30 units
More liquid spreads the same milligrams over more units, so small amounts sit on more syringe lines and are easier to read, but every dose takes more volume. Less liquid does the opposite. The volume to use should come from the instructions supplied with the vial or from a pharmacist; this page only shows what each choice means in units.
Tables for common vial sizes
Find your vial size in the rows and the total solution volume in the columns. To get units for your dose, multiply the second table's number by the dose in mg: 2.5 mg from a 10 mg vial with 2 mL is 2.5 × 20 = 50 units.
| Vial | 1 mL | 1.5 mL | 2 mL | 2.5 mL | 3 mL |
|---|---|---|---|---|---|
| 5 mg | 5 | 3.333 | 2.5 | 2 | 1.667 |
| 10 mg | 10 | 6.667 | 5 | 4 | 3.333 |
| 12 mg | 12 | 8 | 6 | 4.8 | 4 |
| 15 mg | 15 | 10 | 7.5 | 6 | 5 |
| 20 mg | 20 | 13.333 | 10 | 8 | 6.667 |
| 24 mg | 24 | 16 | 12 | 9.6 | 8 |
| 30 mg | 30 | 20 | 15 | 12 | 10 |
| Vial | 1 mL | 1.5 mL | 2 mL | 2.5 mL | 3 mL |
|---|---|---|---|---|---|
| 5 mg | 20 | 30 | 40 | 50 | 60 |
| 10 mg | 10 | 15 | 20 | 25 | 30 |
| 12 mg | 8.33 | 12.5 | 16.67 | 20.83 | 25 |
| 15 mg | 6.67 | 10 | 13.33 | 16.67 | 20 |
| 20 mg | 5 | 7.5 | 10 | 12.5 | 15 |
| 24 mg | 4.17 | 6.25 | 8.33 | 10.42 | 12.5 |
| 30 mg | 3.33 | 5 | 6.67 | 8.33 | 10 |
Values are rounded for display; the calculator works from the unrounded numbers. Volumes assume the total solution is the water added, which is a close approximation.
What "reconstituting" changes in the math
Freeze-dried vials hold powder until liquid is added. The amount of liquid is the only part of reconstitution that changes the arithmetic: it fixes the concentration for the life of the vial. If you're unsure how much liquid a vial holds, don't guess from the label size; ask the pharmacist who supplied it. How to add the liquid, keep it sterile and store it are questions for a pharmacist, not a calculator.
Retatrutide's status
Questions
How many units is 1 mg of retatrutide?
It depends on the vial and the volume, not on retatrutide itself. From a 10 mg vial holding 2 mL (5 mg/mL), 1 mg is 0.2 mL, or 20 units. From the same vial holding 1 mL, it's 10 units; holding 3 mL, it's 30 units. The table above lists every common combination.
How much bac water for a 10 mg retatrutide vial?
There's no single correct amount in the math: the volume you add sets the concentration. 1 mL gives 10 mg/mL, 2 mL gives 5 mg/mL and 3 mL gives about 3.33 mg/mL. The amount should come from the instructions supplied with the vial or from a pharmacist. Once you know it, the calculator turns your dose into units.
How many units is 2 mg from a 12 mg vial?
With 2 mL of solution the vial is 6 mg/mL, so 2 mg is 2 ÷ 6 = 0.333 mL, or 33.3 units. With 3 mL it's 4 mg/mL, so 2 mg is 0.5 mL, or 50 units. Enter your own numbers above to check.
Is retatrutide FDA approved?
No. As of November 2026 retatrutide is an investigational medicine from Eli Lilly and isn't approved by the FDA for any use. Lilly has said it plans to apply for approval in 2027. Products sold online as retatrutide are not the approved or trial medicine, and their contents aren't verified.
Is GLP-3 the same as retatrutide?
"GLP-3" is an informal nickname, often used by sellers, not a scientific name. There's no GLP-3 hormone. Retatrutide acts on three receptors, GIP, GLP-1 and glucagon, which is where the "3" comes from. A product's nickname tells you nothing about what's in the vial.
Does the calculator include trial doses?
No. Trial doses describe what participants received in a study under medical supervision; they aren't a schedule for anyone else. Doses here are always the number you type in.