Peptide reconstitution calculator
Reconstitution is one division. This does it for you, then converts the result into the mark on your syringe.
How the maths works
Every reconstitution calculation is the same three steps, and once you have seen them you can check any calculator's answer by hand.
Step one, concentration. Divide the peptide in the vial by the water you added. A 10 mg vial with 2 mL of bacteriostatic water is 10 / 2 = 5 mg per mL.
Step two, volume. Divide your dose by that concentration. A 2 mg dose at 5 mg/mL is 2 / 5 = 0.4 mL.
Step three, units. A standard U-100 insulin syringe holds 100 units in 1 mL, so multiply the volume by 100. 0.4 mL is 40 units, which is the 40 mark on the barrel.
The one that catches people out is U-40 syringes, which are usually veterinary. They hold 40 units in 1 mL, so the same 0.4 mL is 16 units, not 40. Check which scale is printed on your barrel before you draw.
How much bacteriostatic water should I add?
There is no single correct amount. The water does not change the dose, only how far along the barrel that dose lands. More water means a bigger, easier-to-read draw of a weaker solution. Less water means a small, concentrated draw that is harder to measure precisely.
The practical rule is to pick a volume that puts your usual dose somewhere between roughly 10 and 50 units, because that part of the barrel is easy to read and small errors matter least. If the calculator tells you to draw 3 units, add more water. If it tells you to draw 90 units, add less.
Whatever you choose, write it on the vial. The number is meaningless a week later if you cannot remember how much water went in, and that is the single most common reason people end up re-dosing wrong.
The same 2 mg dose, at four different water volumes
This is the point people miss. The dose below never changes. Only the water does, and it moves the draw from an unreadable sliver to most of the barrel.
| Vial | BAC water | Concentration | Draw | U-100 units | Doses/vial |
|---|---|---|---|---|---|
| 10 mg | 1 mL | 10 mg/mL | 0.2 mL | 20 units | 5 |
| 10 mg | 2 mL | 5 mg/mL | 0.4 mL | 40 units | 5 |
| 10 mg | 3 mL | 3.33 mg/mL | 0.6 mL | 60 units | 5 |
| 10 mg | 4 mL | 2.5 mg/mL | 0.8 mL | 80 units | 5 |
All rows above assume a 2 mg dose and a standard U-100 insulin syringe, where 100 units = 1 mL.
Calculators by compound
Common questions
- What does reconstituting a peptide mean?
- Peptides are shipped as a freeze-dried powder. Reconstituting means adding bacteriostatic water to dissolve the powder into a solution you can draw into a syringe. The water is the only thing you control, and it sets the concentration.
- How much bacteriostatic water do I add to a 10 mg vial?
- Any amount the vial physically holds. 2 mL is the most common choice for a 10 mg vial because it gives 5 mg/mL, which puts most doses in an easy to read part of the barrel. 1 mL doubles the concentration and halves the units you draw.
- Can I use normal water or saline instead?
- Bacteriostatic water contains benzyl alcohol, which is what lets a vial be entered repeatedly over weeks. Sterile water and saline have no preservative, so a vial reconstituted with them is single use.
- How long does a reconstituted vial last?
- It depends on the compound, the storage temperature and the water used. Manufacturers' figures vary widely. Store reconstituted vials refrigerated and check the guidance for your specific compound.