How to mix a vial
- Find the water: enter your vial, your dose and the units you want per dose above, or read the table below.
- Draw that much water into a syringe.
- Inject it into the vial with the stream aimed at the glass wall, not at the powder, so it does not foam.
- Swirl the vial gently until the powder has dissolved. Do not shake it.
- Use the mix only if it is clear, with no cloudiness or particles.
- Write the concentration and the date mixed on the vial: Print label above prints the concentration with a line for the date.
Steps 3 to 5 are the handling the Serostim and Omnitrope labels give for their freeze-dried somatropin.
Water for common vial sizes
Your dose divided by the amount in a cell is the units to draw.
| Vial | 1 mL water | 2 mL water | 3 mL water |
|---|---|---|---|
| 2 mg | 20 mcg | 10 mcg | 6.7 mcg |
| 5 mg | 50 mcg | 25 mcg | 16.7 mcg |
| 10 mg | 100 mcg | 50 mcg | 33.3 mcg |
| 15 mg | 150 mcg | 75 mcg | 50 mcg |
| 20 mg | 200 mcg | 100 mcg | 66.7 mcg |
| 30 mg | 300 mcg | 150 mcg | 100 mcg |
Sterile or bacteriostatic water
Sterile Water for Injection has no preservative. On the Serostim label, a vial mixed with it is used at once, for one dose, and the rest is thrown away.
Bacteriostatic Water for Injection holds 0.9% benzyl alcohol as a preservative, and the same label lets a Serostim 4 mg vial mixed with it be kept in a refrigerator at 2 to 8 °C (36 to 46 °F) for up to 14 days. The label uses sterile water instead for anyone allergic to benzyl alcohol, and in pregnancy and breast-feeding. Omnitrope, mixed with its own preserved diluent, is used within 21 days.
Choosing the units per dose
The water sets how much peptide each unit holds; the dose stays the same. More water makes the mix weaker, so the same dose takes more units, which is easier to read for a small dose. Less water keeps a large dose within one syringe.
The example in the calculator. A 5 mg vial, a 250 mcg dose, 10 units per dose. 10 units is 0.1 mL, so the mix must hold 0.25 mg in 0.1 mL: 2.5 mg per mL. 5 mg at 2.5 mg per mL is 2 mL of water.
Pick units that sit on a line of your syringe: every unit on 0.3 and 0.5 mL syringes, every 2 units on many 1 mL syringes. If you have already added the water, the peptide calculator gives the units for the water in the vial.
For a reusable U-100 pen, choose Pen under Measure with. All the mix goes into the cartridge, so the water can be at most what the cartridge holds, 3 mL on every pen in the list, and each dose also uses a priming shot: with the example, 2 mL of mix gives 200 units, and 200 ÷ (10 + 2) is 16 doses.
Other calculators
- Insulin syringe units to mLUnits on a U-100 insulin syringe in mL, and mL in units.
- Semaglutide units to mgThe mg in the units you draw of a semaglutide vial, or the units for a dose, from the strength printed on the vial.
- HGH reconstitution calculatorUnits to draw for an HGH dose in IU or mg, from the vial and the water you added.
- NAD+ injection calculatorUnits to draw for an NAD+ dose, from the mg in the vial and the mL of liquid in it.
- How much bacteriostatic water for 10 mg retatrutideThe water to add to a 10 mg retatrutide vial so your dose is the number of units you want to draw.
- How much bacteriostatic water for 30 mg retatrutideThe water to add to a 30 mg retatrutide vial so your dose is the number of units you want to draw.
Questions
How much water goes into a 5 mg vial?
As much as puts your dose on a line you can read. With 1 mL each unit holds 50 mcg, with 2 mL 25 mcg, with 3 mL 16.7 mcg. Enter your dose and the units you want above for the exact amount.
How much water goes into a 10 mg vial?
With 1 mL each unit holds 100 mcg, with 2 mL 50 mcg, with 3 mL 33.3 mcg. The calculator above works out the water for the units you want per dose.
Does more water change the dose?
No. The peptide in the vial stays the same; more water spreads it over more units, so the same dose takes more units and the vial holds the same number of doses.
What if I added a different amount of water?
Use the amount you added. The peptide calculator takes the vial, the water in it and your dose, and gives the units to draw.
Sources
- Serostim (somatropin) for injection, prescribing informationFDA, label of 2026-07-29. 2.2 Preparation and Administration: the diluents, the stream against the vial wall, swirl and do not shake, 14 days refrigerated with bacteriostatic water.
- Omnitrope (somatropin) injection and for injection, prescribing informationFDA, label of 2025-07-11. Swirl gently, do not shake; use only if clear; the mixed vial used within 21 days.
- BD Insulin Syringe, 510(k) K190054FDA, cleared 2019-10-21. U-100 syringes of 0.3, 0.5 and 1 mL and their lines.