Last updated: May 2026

Peptide Dosage & Reconstitution Calculator

Quick answer: A 5 mg vial reconstituted with 10 mL of bacteriostatic water gives 500 mcg/mL, so a 250 mcg dose = 0.50 mL = 50 units on a U-100 syringe. Formula: concentration = vial content (mcg) ÷ BAC water (mL); draw volume = dose ÷ concentration.

About this calculator

The peptide reconstitution calculator derives vial concentration from the amount of bacteriostatic water added (Concentration = Vial content (mcg) ÷ BAC water (mL)), then converts a target dose to draw volume (Volume = Dose ÷ Concentration). Built for anyone preparing lyophilised peptide vials for injection with a U-100 insulin syringe. Works for any freeze-dried peptide. Free, instant, no login.

How to use this calculator

You need your vial size in milligrams (printed on the vial — e.g., 5mg), your target concentration in mcg/mL, and your dose in mcg per injection.

Enter the vial size and target concentration first — the calculator shows how much bacteriostatic water to inject into the vial. Then enter your dose per injection to see exactly how many mL and how many U-100 syringe units to draw each time.

If you are unsure what concentration to use, a common starting point for a 5mg vial is 500mcg/mL, which requires 10mL of BAC water. This gives manageable injection volumes for doses in the 250–500mcg range.

Worked example — BPC-157 5mg vial

Reconstitution

Vial size: 5 mg (5,000 mcg)

Target concentration: 500 mcg/mL

BAC water to add = 5,000 ÷ 500 = 10 mL

Per-injection dose — 250 mcg

Concentration: 500 mcg/mL

Dose: 250 mcg

Draw = 250 ÷ 500 = 0.50 mL = 50 units on a U-100 syringe

How to interpret your result

The BAC water volume is the amount of bacteriostatic water to inject slowly into the vial using a sterile syringe. Inject it down the side of the vial — never directly onto the peptide powder — and swirl gently. Do not shake.

The units result is what you read on a U-100 (100-unit insulin) syringe. U-100 syringes are marked in units, not mL — 100 units equals 1mL, so 50 units equals 0.5mL.

Store reconstituted peptides refrigerated at 2–8°C. Most peptides are stable for 30 days once reconstituted, though stability varies — check the specific data for your peptide.

Common reconstitution volumes for a 5mg vial

BAC water added	Concentration	250 mcg dose	500 mcg dose
2 mL	2,500 mcg/mL	10 units	20 units
5 mL	1,000 mcg/mL	25 units	50 units
10 mL	500 mcg/mL	50 units	100 units

Frequently asked questions

Does it matter how much BAC water I add?

Yes — the amount determines your concentration, which directly affects how many units you draw per dose. Using less BAC water gives a higher concentration and smaller injection volumes. Using more gives a lower concentration and larger volumes. There is no single correct amount; it depends on your dose range and syringe preference.

Can I use sterile water instead of bacteriostatic water?

Sterile water has no preservative, so it is only suitable for single-use reconstitution. Bacteriostatic water (with 0.9% benzyl alcohol) is preferred for multi-dose vials because it inhibits bacterial growth over multiple punctures.

How long does reconstituted peptide last?

Most peptides are stable for approximately 30 days when refrigerated at 2–8°C after reconstitution with bacteriostatic water. Stability varies by peptide — some are more fragile. Freeze the vial before reconstitution for longer storage.

What is a U-100 syringe?

A U-100 syringe is a standard insulin syringe calibrated for U-100 insulin (100 units per mL). The unit markings on the barrel correspond directly: 100 units = 1mL, 50 units = 0.5mL. They are commonly used for subcutaneous peptide injections because of the small gauge needle and precise markings.

What concentration should I use for my peptide vial?

A common starting point is 500 mcg/mL for a 5 mg vial — that means adding 10 mL of bacteriostatic water. At this concentration a 250 mcg dose = 50 units and a 500 mcg dose = 100 units on a U-100 syringe. Use a higher concentration (less BAC water) if you prefer smaller injection volumes; use a lower concentration if your doses are large relative to your syringe size. The calculator above works out the maths for any combination.

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How this is calculated

This calculator divides your prescribed dose by the vial concentration to find the injection volume, then converts that volume to insulin-syringe units (volume in mL × 100 for a U-100 syringe). It is arithmetic only — nothing you enter is stored or sent anywhere, and the result is not medical advice. Always confirm your dose with your prescriber.