A worked example
Say your vial contains 5 mg of peptide, you add 2 mL of bacteriostatic water, and your dose is 250 mcg.
- Find the concentration. 5 mg is 5,000 mcg. Divided by 2 mL, that is 2,500 mcg per mL.
- Find the volume for one dose. 250 mcg ÷ 2,500 mcg/mL = 0.1 mL.
- Convert to units. A U-100 syringe has 100 units per mL, so 0.1 mL = 10 units.
- Count doses. 5,000 mcg ÷ 250 mcg = 20 doses in the vial.
Concentration (mcg/mL) = vial amount in mcg ÷ water in mL
Units to draw = dose in mcg ÷ concentration × 100
Water to add (mL) = units you want × vial mcg ÷ (dose mcg × 100)
Concentration chart: mcg per unit
Each cell shows how many micrograms are in one unit (0.01 mL) for a given vial size and water volume. Multiply by the units you draw to get the dose, or divide your dose by the cell to get units.
| Vial | 1 mL water | 2 mL water | 3 mL water |
|---|---|---|---|
| 2 mg | 20 mcg/unit | 10 mcg/unit | 6.67 mcg/unit |
| 5 mg | 50 mcg/unit | 25 mcg/unit | 16.67 mcg/unit |
| 10 mg | 100 mcg/unit | 50 mcg/unit | 33.33 mcg/unit |
| 15 mg | 150 mcg/unit | 75 mcg/unit | 50 mcg/unit |
| 20 mg | 200 mcg/unit | 100 mcg/unit | 66.67 mcg/unit |
Example: a 10 mg vial with 2 mL of water gives 50 mcg per unit, so a 500 mcg dose is 500 ÷ 50 = 10 units.
Mistakes the calculator helps you avoid
Common errors
- Entering mg where the label says mcg, or the other way round (a 1,000× error).
- Using a U-40 syringe with U-100 math. Check the label on the syringe pack.
- Forgetting that the water volume changes the concentration.
- Reading half-unit lines on a 0.3 mL syringe as full units.
Good habits
- Write the concentration on the vial label after mixing.
- Pick a water volume that makes doses land on whole units.
- Use the smallest syringe that fits the dose; its markings are easier to read.
- Re-check the math any time you switch vial size.
New to mixing? Read how to reconstitute peptides for the full process, and the insulin syringe units chart to learn how each syringe size is marked.
Important
This site does arithmetic. It cannot tell you what dose to use, whether a product is safe or legal for you, or how to inject. Follow the instructions from your prescriber or pharmacist and the product's own documentation.
Frequently asked questions
How do I use the peptide reconstitution calculator?
Enter the amount of peptide in the vial (for example 5 mg), how much bacteriostatic water you add (for example 2 mL), and the dose you were told to take (for example 250 mcg). Pick your syringe size. The calculator shows how many units to draw on a U-100 insulin syringe, the same amount in mL, the concentration, and how many doses the vial holds.
How many units is 250 mcg?
It depends on the concentration. With a 5 mg vial mixed with 2 mL of water, the solution is 2,500 mcg per mL, so 250 mcg is 0.1 mL, which is 10 units on a U-100 syringe. Mix the same vial with 1 mL and 250 mcg becomes 5 units. Always calculate from your own vial size and water volume.
What does "units" mean on an insulin syringe?
A U-100 insulin syringe is marked so that 100 units equals 1 mL. One unit is therefore 0.01 mL. The markings measure volume, not the amount of any particular substance, which is why you need the concentration to turn a dose in mcg or mg into units.
How much bacteriostatic water should I add?
There is no single correct amount; it is a trade-off. More water makes each dose a larger, easier-to-measure volume. Less water keeps doses small. Use the "How much water?" tab: enter the dose and the number of units you would like to draw each time, and it tells you how much water gives exactly that.
What is the difference between mg and mcg?
One milligram (mg) is 1,000 micrograms (mcg). Mixing them up is the most common and most dangerous error in reconstitution math, because it changes the result by a factor of 1,000. Check the unit on your vial label and on your instructions before you enter anything.
Can I use this for any peptide?
The math is the same for any powder dissolved in a liquid, so the calculator works for any vial size and water volume. It does not know anything about specific products or what dose is appropriate. That information must come from your prescriber, pharmacist or the product documentation.