What does a peptide dosage chart by vial size actually show?

It maps a vial's labeled mg amount and the water volume added to it into a concentration (mcg/mL) and a syringe-unit value (mcg per unit on a U-100 scale). The vial size alone does not set your dose — the water volume you add does.

Does a bigger vial mean a bigger dose?

No. Vial size sets the total mg of peptide available across the whole vial, not the size of a single dose. A 20 mg vial mixed with more water can produce the same per-dose concentration as a 5 mg vial mixed with less water.

How much bacteriostatic water should I add to a 10 mg vial?

It depends on the concentration you want. 10 mg in 1 mL gives 10,000 mcg/mL; 10 mg in 2 mL gives 5,000 mcg/mL. More water lowers the concentration and produces a larger, easier-to-read draw for the same dose.

Peptide Dosage Chart by Vial Size

By PeptCalc Research — Medically reviewed by David Mansour, MD — Last reviewed July 12, 2026

Vial size alone does not tell you how many units to draw. The mg amount printed on the label, combined with how much bacteriostatic water you add, sets the concentration — and concentration is what turns a target dose into a syringe-unit count. This chart lays out that math for common vial sizes. It is a reference for research and educational purposes only and is not medical advice.

Why vial size isn't the whole picture

Two vials of different sizes can produce an identical dose in an identical number of units, as long as their concentrations match. A 5 mg vial in 1 mL and a 10 mg vial in 2 mL are both 5,000 mcg/mL — the larger vial just holds more total doses at that same strength. The variable that matters for any single draw is concentration (mg or mcg per mL), not the number printed on the vial.

Dosage chart by vial size

Each row shows a common vial size, a water volume that produces a clean concentration, and the resulting mcg per unit on a U-100 insulin syringe (100 units per mL, so mcg per unit = concentration ÷ 100).

Vial size	Water added	Concentration	mcg per unit
2 mg	1 mL	2,000 mcg/mL	20 mcg
2 mg	2 mL	1,000 mcg/mL	10 mcg
5 mg	1 mL	5,000 mcg/mL	50 mcg
5 mg	2 mL	2,500 mcg/mL	25 mcg
10 mg	1 mL	10,000 mcg/mL	100 mcg
10 mg	2 mL	5,000 mcg/mL	50 mcg
10 mg	5 mL	2,000 mcg/mL	20 mcg
15 mg	1 mL	15,000 mcg/mL	150 mcg
15 mg	3 mL	5,000 mcg/mL	50 mcg
15 mg	5 mL	3,000 mcg/mL	30 mcg
20 mg	2 mL	10,000 mcg/mL	100 mcg
20 mg	4 mL	5,000 mcg/mL	50 mcg
20 mg	5 mL	4,000 mcg/mL	40 mcg

These water volumes were chosen because they land on round mcg-per-unit figures. Any volume works mathematically — the reconstitution calculator handles volumes that don't produce clean numbers and its reverse mode finds a volume that does.

Reading the chart against a target dose

Once you know mcg per unit, converting a target dose is one division:

Units to draw = target dose (mcg) ÷ mcg per unit

Worked example. A 15 mg vial mixed with 3 mL of water sits at 5,000 mcg/mL, or 50 mcg per unit. A 300 mcg dose from that vial is 300 ÷ 50 = 6 units. The same 300 mcg dose from a 20 mg vial in 4 mL — also 50 mcg per unit — is also 6 units, despite the larger vial.

Worked example, different concentration. A 5 mg vial mixed with 1 mL sits at 5,000 mcg/mL, or 50 mcg per unit too — so the same 300 mcg dose is again 6 units. What changes across these three examples is how many total doses each vial holds, not the units for a single draw.

Choosing a water volume for a given vial

The reconstitution step, not the injection, is where a dosage figure typically goes wrong: the water volume sets the concentration, and every unit count downstream is only as accurate as that one number. This is fixed arithmetic — verifiable against any U-100 syringe specification — which is why the reconstitution calculator exists: it removes the one manual calculation that determines every dose that follows.

When picking a volume for a vial not shown above, aim for a concentration that puts your typical dose on a whole or easily-read unit mark, rather than a fraction that's hard to see on the barrel. The insulin syringe unit guide covers reading unit marks on 0.3 mL, 0.5 mL, and 1 mL syringes.

Common mistakes

Assuming vial size determines dose size. It determines total mg available; water volume determines concentration, and concentration determines units per dose.
Mixing up mg and mcg. 1 mg equals 1,000 mcg — the most common source of a 1,000x error when reading a chart like this one.
Reusing a unit count across a different vial or water volume. A unit count is only valid for the exact concentration it was calculated from.
Shaking rather than swirling during reconstitution, which can affect the peptide before concentration is even relevant. See how to reconstitute peptides for the mixing steps.

Enter any vial size and target dose into the peptide reconstitution calculator for an exact unit count, or use its reverse mode to find a water volume that lands your dose on a round syringe mark. For the mixing procedure itself, see how to reconstitute peptides; for reading the syringe barrel, see how to read insulin syringe units for peptides.