Reconstitution, explained
Last reviewed 2026-06-11 · 6 min read
Bottom line: reconstitution is three divisions. Concentration = peptide ÷ water. Dose volume = dose ÷ concentration. Syringe units = volume × 100. Everything else is unit conversion — and the calculator does all of it.
What reconstitution is
Most research peptides ship as a lyophilized (freeze-dried) powder in a small vial. Before it can be drawn into a syringe, the powder is dissolved in a measured amount of bacteriostatic water. That measured amount is the single most important number you'll write down: it sets the concentration, and the concentration decides what every mark on your syringe means.
The three numbers
| Number | Formula | Example (5 mg vial + 2 mL water) |
|---|---|---|
| Concentration | peptide ÷ water | 5 mg ÷ 2 mL = 2.5 mg/mL |
| Dose volume | dose ÷ concentration | 250 mcg ÷ 2,500 mcg/mL = 0.1 mL |
| Syringe units | volume × 100 | 0.1 mL = 10 units (U-100) |
The "× 100" works because a U-100 insulin syringe is defined as 100 units per mL — that's what U-100 means. A 0.5 mL syringe holds 50 units; a 0.3 mL holds 30. The units are a volume scale, nothing more.
Worked example, end to end
Say a vial holds 10 mg of a peptide, and the target dose is 500 mcg.
- Add 3 mL of bacteriostatic water → concentration is 10 ÷ 3 ≈ 3.33 mg/mL (3,333 mcg/mL).
- Dose volume: 500 ÷ 3,333 ≈ 0.15 mL.
- Draw to 15 units on a U-100 syringe. The vial holds 10,000 ÷ 500 = 20 doses.
Choosing how much water
More water = more dilute = more units per dose, which is easier to measure accurately. Less water = concentrated = small draws, which fit small syringes but amplify any measuring error. Two rules of thumb keep you out of trouble:
- Pick a volume that puts your usual dose between roughly 5 and 30 units — big enough to measure, small enough to leave headroom.
- Pick a round number that makes the mental math clean (1, 2 or 3 mL beats 1.7 mL).
The classic mistakes
- Forgetting the water amount. Without it, the vial is a mystery solution. Write it on the vial or log it the moment you reconstitute.
- mg/mcg confusion. 1 mg = 1,000 mcg. Most dosing errors are a thousand-fold unit slip — sanity-check that your dose volume is a fraction of a mL, not multiple mL.
- Assuming all syringes are U-100. They almost always are, but check the barrel — the math above is U-100 math.
- Spraying water directly onto the powder. Run it down the glass wall slowly and swirl gently; peptides are fragile molecules and foaming degrades some of them.
- Skipping the fridge. Most reconstituted peptides are stored cold — check the compound library entry for storage notes.
Track it once, reuse it every pin
This math only needs doing once per vial — if it's logged. Stack stores the vial size and water volume when you add a vial, shows the unit draw for your scheduled dose, counts doses remaining and projects the refill date. Get the app →