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Peptide reconstitution calculator
Work out exactly how many units to draw, the concentration, and how many doses you'll get per vial — and the best water amount to land your dose on a clean syringe mark.
Your vial and dose
Example numbersDraw to
40unitson a U-100 syringe
Lands on a numbered mark
- Concentration
- 5 mg/mL5,000 mcg/mL
- Doses per vial
- 5
How reconstitution math works
Reconstitution is mixing a lyophilized (freeze-dried) peptide with bacteriostatic water so you can draw an accurate dose. The units you draw follow one formula: units = dose (mcg) × water (mL) ÷ (vial mg × 10).
A useful thing to know: the amount of water doesn't change how many doses are in the vial — it only changes the concentration, i.e. how many units you draw for the same dose. More water means a larger, easier-to-read draw on the syringe.
Example: a 10 mg vial mixed with 2 mL of bacteriostatic water is 5 mg/mL, so a 2 mg dose is 40 units on a U-100 syringe, and the vial holds 5 doses.
Reconstitution math: common questions
Worked arithmetic for reference, not a dose recommendation.
How much bacteriostatic water should I add to a 10 mg vial?
The water sets the concentration, not how much peptide is in the vial. A 10 mg vial holds 10,000 mcg: with 1 mL of water that's 10,000 mcg/mL (100 mcg per unit on a U-100 syringe), with 2 mL it's 5,000 mcg/mL (50 mcg per unit), and with 3 mL it's about 3,333 mcg/mL (about 33 mcg per unit). A practical way to choose is the volume that puts the dose you're tracking on an easy-to-read syringe mark. Enter your vial, water and dose above and the calculator suggests one.
How many units is 250 mcg from a 5 mg vial mixed with 2 mL of water?
10 units. 5 mg is 5,000 mcg, so 2 mL of water makes 2,500 mcg/mL, which is 25 mcg per unit on a U-100 syringe, and 250 mcg ÷ 25 mcg per unit = 10 units. The general formula is units = dose (mcg) × water (mL) ÷ (vial mg × 10).
How do I work out the concentration of a reconstituted vial?
Concentration (mcg/mL) = vial mg × 1,000 ÷ water mL. A 5 mg vial with 2 mL of water is 2,500 mcg/mL; the same vial with 2.5 mL is 2,000 mcg/mL. Because 100 units on a U-100 insulin syringe equal 1 mL, each unit holds the concentration ÷ 100, so 25 mcg per unit at 2,500 mcg/mL.
Does adding more water change how many doses are in a vial?
No. Doses per vial = vial mcg ÷ dose mcg, whatever the water volume. A 10 mg vial holds forty 250 mcg doses whether you add 1 mL or 3 mL. More water only makes each dose a larger draw, which is easier to read on the syringe.
What is a unit on an insulin syringe?
On a U-100 insulin syringe, 100 units equal 1 mL, so 1 unit is 0.01 mL. Units measure volume, not dose: how much peptide each unit holds depends on how the vial was reconstituted.
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