Reconstitution is arithmetic, and the arithmetic is simple enough that the errors come from mixing units rather than from the maths. This calculator does the three steps in order: mass over volume gives a concentration, the target amount divided by that concentration gives a volume, and that volume read against the hundredth-millilitre marks of a U-100 syringe gives units.

Change any field and the numbers update. The presets match common vial sizes.

mL
Concentration
5 mg/mL
5000 mcg in every 1 mL
Volume per draw0.05 mL
On a U-100 syringe5 units
Draws per vial40
Total in vial10 mg
050100 units

How this is calculated. Concentration is the peptide mass divided by the volume of bacteriostatic water added — the powder itself contributes negligible volume. The volume per draw is the target amount divided by that concentration. A U-100 syringe is marked in hundredths of a millilitre, so 1 unit is 0.01 mL regardless of barrel size. Nothing here is guidance for use in people: Soraci Labs products are sold for laboratory research use only.

The three steps, written out

  • Concentration = peptide mass ÷ water added. 10 mg into 2 mL is 5 mg/mL.
  • Volume per draw = target amount ÷ concentration. 250 mcg is 0.25 mg, and 0.25 ÷ 5 is 0.05 mL.
  • Syringe units = volume × 100. 0.05 mL is 5 units on any U-100 barrel.

The one trap worth naming: milligrams and micrograms differ by a factor of a thousand, and most mistakes in this calculation are a decimal place rather than a misunderstanding. Set both unit dropdowns deliberately rather than assuming.

Choosing how much water to add

The volume is a free choice, and it is the choice that decides how readable your measurements are. The same 10 mg vial reconstituted with 1 mL puts a 250 mcg draw at 2.5 units; with 3 mL it puts the same draw at 7.5 units. Nothing about the peptide changed — only how far apart the marks are.

Below roughly two units the barrel becomes hard to read honestly, which is why the calculator flags it. Above the barrel capacity you simply cannot draw the amount at all, and the fix is the same in reverse: less water.

Frequently asked questions

How do I calculate peptide concentration after reconstitution?
Divide the mass of peptide in the vial by the volume of bacteriostatic water you add. A 10mg vial reconstituted with 2mL gives 5 mg/mL, which is 5000 mcg per millilitre. The powder itself adds negligible volume, so the water you add is the volume.
What does one unit on an insulin syringe equal?
A U-100 syringe is marked in hundredths of a millilitre, so one unit is 0.01 mL. That holds whether the barrel is 0.3mL, 0.5mL or 1mL — only the number of marks changes, not what each mark means.
How much bacteriostatic water should I add?
There is no single right answer: the water sets the concentration, and the concentration sets how many syringe units a given amount occupies. More water spreads the same mass over more volume, which makes small amounts easier to measure accurately. The calculator warns when a draw falls below about two units, where reading the barrel gets imprecise.
Does the peptide powder change the final volume?
Not meaningfully at these masses. A few milligrams of lyophilised solid displaces a negligible fraction of a millilitre, so treating the water added as the final volume is accurate enough for bench work.
Why does my draw need more units than the syringe holds?
The vial is too concentrated for the amount you want. Reconstituting with more water lowers the concentration, so the same mass occupies a larger, measurable volume.

Related reading

All Soraci Labs products are sold for laboratory research use only. They are not drugs, supplements or cosmetics, and are not for human or veterinary use. This calculator performs unit arithmetic and is not guidance for use in people.