Peptide reconstitution calculator
Units to draw = your amount in mcg ÷ (vial mg × 1,000 ÷ water mL) × 100. Enter your own numbers below, or switch to “Water to add” to work backwards from the units you want. The calculator does arithmetic only and never suggests an amount.
Enter your numbers to see the result.
This calculator does arithmetic. It does not recommend an amount.
How the math works
| Step | What you do | Formula |
|---|---|---|
| 1. Find the concentration | Multiply the vial’s mg by 1,000 to get mcg, then divide by the mL of water you added. That gives mcg per mL. | mcg/mL = mg × 1000 ÷ mL |
| 2. Convert your amount to mL | Divide the amount your clinician set (in mcg) by the concentration. That is the volume to draw. | mL = amount ÷ mcg/mL |
| 3. Convert mL to syringe units | A U-100 syringe has 100 units per mL, so multiply the mL by 100. | units = mL × 100 |
| Reverse | To make your amount equal a chosen number of units, solve for the water. | mL water = vial mcg × units ÷ (amount × 100) |
How much water to add: what it changes
Water only sets the concentration. The amount of peptide in the vial stays the same. More water means each unit holds less, which makes small amounts easier to read, but each injection is a larger volume. The table shows the arithmetic for common vial sizes; it is math, not a dose recommendation.
| Vial | 1 mL water | 2 mL water | 2.5 mL water | 3 mL water |
|---|---|---|---|---|
| 2 mg | 2 mg/mL 20 mcg/unit | 1 mg/mL 10 mcg/unit | 0.8 mg/mL 8 mcg/unit | 0.67 mg/mL 6.7 mcg/unit |
| 5 mg | 5 mg/mL 50 mcg/unit | 2.5 mg/mL 25 mcg/unit | 2 mg/mL 20 mcg/unit | 1.67 mg/mL 16.7 mcg/unit |
| 10 mg | 10 mg/mL 100 mcg/unit | 5 mg/mL 50 mcg/unit | 4 mg/mL 40 mcg/unit | 3.33 mg/mL 33.3 mcg/unit |
| 15 mg | 15 mg/mL 150 mcg/unit | 7.5 mg/mL 75 mcg/unit | 6 mg/mL 60 mcg/unit | 5 mg/mL 50 mcg/unit |
Reading a U-100 syringe
| Syringe | Holds | 1 unit equals |
|---|---|---|
| 0.3 mL | 30 units | 0.01 mL |
| 0.5 mL | 50 units | |
| 1 mL | 100 units |
All three use the same scale. The smaller barrels are shorter, so small volumes are easier to read.
Common mistakes
- mg vs mcg. 1 mg is 1,000 mcg. The calculator flags amounts that only make sense in the other unit.
- The wrong syringe. These units only apply to U-100 insulin syringes.
- Going over the barrel. The calculator warns when the draw is more than the syringe you picked holds.
- Tiny draws. Under 2 units is hard to measure; more water spreads the same amount over more units.
How to reconstitute a vial
- Clean the stoppers. Wipe the rubber stopper of the peptide vial and the water vial with an alcohol swab and let them dry.
- Draw the water. Draw the volume of bacteriostatic water you chose into a sterile syringe.
- Add it slowly. Inject the water into the peptide vial so it runs down the inside wall instead of hitting the powder directly.
- Swirl, don’t shake. Swirl or roll the vial gently until the powder dissolves. Shaking can foam the solution.
- Label the vial. Write the concentration and the discard date on the vial. The Joint Commission recommends labeling with the discard date.
- Refrigerate. Store the mixed vial in the fridge and follow the product label or your pharmacy’s date.
How long a mixed vial lasts is covered in how long reconstituted peptides last.
Peptide-specific calculators
FAQ
Is 10 units the same as 0.1 mL?
How many units is a given mcg amount?
Can I use sterile water instead of bacteriostatic water?
What if my draw is under 2 units?
Sources
- USP General Chapter <797> revision notice (USP-NF, 2020)
- The Joint Commission: Medication Management, multiple-dose vial FAQ
Labeling with the discard date: Joint Commission.
This is a math tool, not medical advice. Your clinician decides what amount, if any, is right for you. For prescribed products, use the dose on your prescription and follow your pharmacy.