How peptide reconstitution math works
The calculator above does this for you. This is what it is doing, so you can check it yourself.
What reconstitution actually is
A lyophilized peptide arrives as a freeze-dried powder. Reconstituting it means adding bacteriostatic water so it becomes a liquid you can measure. The amount of peptide never changes when you do this. A 10 mg vial holds 10 mg whether you add 1 mL of water or 5 mL.
What the water changes is concentration, which is how much peptide sits in each millilitre. That decides how far up the syringe your dose lands. More water spreads the same peptide across more liquid, so any given dose is drawn to a higher mark and is easier to measure accurately. Less water does the opposite.
The three numbers you need
- Peptide in the vial — printed on the label, in mg.
- Bacteriostatic water you add — your choice, in mL.
- Your target dose — in mg or mcg.
From those three, everything else is arithmetic.
What a "unit" means
Insulin syringes are marked in units, not millilitres. On a U-100 syringe, 100 units = 1 mL, so one unit is one hundredth of a millilitre. When the calculator tells you to draw to 25 units, it means a quarter of a millilitre.
This is the step people most often get wrong, because the syringe never mentions mg or mcg. It only counts volume. The peptide amount is something you work out from the concentration.
The arithmetic
One conversion catches people out: 1 mg = 1000 mcg. A dose written as 250 mcg is 0.25 mg. Mixing the two up moves the answer by a factor of a thousand, which is why the calculator asks which unit you meant.
A worked example
Say the numbers are a 10 mg vial, 2 mL of bacteriostatic water, and a target of 250 mcg. These are arbitrary figures picked to show the working, not a suggestion.
So you draw to the 5 unit mark, and the vial holds 40 doses of that size.
Choosing how much water to add
There is no single correct amount. It is a trade-off in measurement accuracy, and it is worth thinking about before you mix the vial rather than after.
- Less water gives a higher concentration, so each dose is a very small volume. A draw of 2 or 3 units is hard to measure precisely, and a small error is a large percentage of the dose.
- More water gives a lower concentration and a larger, easier draw. The limit is the syringe: a dose over 100 units will not fit on a U-100 barrel in one go.
The calculator flags both cases. If it warns that the draw is very small, adding less water next time spreads the same dose across more units. If it says the dose exceeds one full syringe, the mix is too dilute for that dose.
Blends and multi-peptide vials
If one vial holds two or three peptides, they share the same water, so a single draw always pulls them in whatever ratio they were mixed. You cannot take more of one and less of another from the same vial. Set your dose for the first peptide and the amounts of the others follow from the mix. The blend calculator underneath the main one works this out.
Related questions
Storage, bacteriostatic water, and what to do if a reconstituted vial looks cloudy are covered on the FAQ. Compound-by-compound information is in the glossary, and the COA guide covers verifying that a vial contains what the label says before any of this math matters.
For educational and research purposes only. Not medical advice. This page explains the arithmetic the calculator performs and does not recommend any dose, compound or protocol. A "unit" refers to the markings on a U-100 insulin syringe (100 units = 1 mL). Always verify independently. 21+.