Guides/Peptide BAC Water Calculator

Peptide BAC Water Calculator

How much bacteriostatic water to add to any peptide vial — and why the answer depends on your target dose and preferred draw amount, not a fixed rule.

Works for BPC-157, TB-500, GHK-Cu, Semaglutide, Tirzepatide, CJC-1295, and all lyophilized peptides.

✦

Use Custom Draw mode — skip the table

Enter your preferred syringe units and get the exact BAC water amount to add. Free peptide calculator →

Why There Is No Single "Right" BAC Water Amount

The amount of BAC water you add determines your concentration, which determines how many units you draw per dose. Common advice like "add 2mL to a 5mg vial" is a reasonable starting point — but it may result in draw amounts that are inconvenient. The calculation should be driven by your preferred draw amount.

That's what Custom Draw mode does: you decide how many units you want to draw, and the calculator tells you how much BAC water to add to make that work exactly.

BAC Water Reference Table

Common vial sizes and BAC water volumes. Draw units for 250mcg and 500mcg doses on a U-100 syringe.

VialBAC WaterConcentration250mcg dose500mcg dose
2mg1mL2,000 mcg/mL12.5 units25 units
2mg2mL1,000 mcg/mL25 units50 units
5mg1mL5,000 mcg/mL5 units10 units
5mg2mL2,500 mcg/mL10 units20 units
5mg3mL1,667 mcg/mL15 units30 units
10mg2mL5,000 mcg/mL5 units10 units
10mg4mL2,500 mcg/mL10 units20 units

U-100 syringe. Use the calculator for other syringe types or dose amounts.

What Is BAC Water?

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol. The benzyl alcohol acts as a preservative, inhibiting bacterial growth and allowing multi-dose vial use for up to 28 days refrigerated.

Do not substitute plain sterile water for multi-dose use — it contains no preservative. Do not use saline, which can cause peptide degradation.

FAQ

How much BAC water do I add to my peptide vial?+
There is no single correct amount — it depends on your target dose and preferred draw. A common starting point for a 5mg vial is 2mL of BAC water, yielding 2,500mcg/mL. At this concentration, 250mcg = 10 units on a U-100 syringe. Protocol's Custom Draw mode calculates the exact BAC water volume based on your preferred draw amount.
What is bacteriostatic water?+
Bacteriostatic water (BAC water) is sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol prevents bacterial growth, allowing the reconstituted vial to be stored for up to 28 days refrigerated. Do not use plain sterile water for multi-dose vials.
What is Custom Draw mode?+
Custom Draw mode in Protocol's peptide calculator lets you specify your preferred syringe draw amount first — for example, 10 units. The calculator then tells you exactly how much BAC water to add so that 10 units delivers your target dose. This is the reverse of standard calculators.
How long does reconstituted peptide last?+
Most reconstituted peptides in bacteriostatic water last 28-30 days refrigerated (2-8°C). Protocol's vial tracker sends low-stock alerts before you run out within the use window.

Calculate Your BAC Water Amount — Free

Custom Draw mode: enter your preferred units, get the exact BAC water volume.

Open Peptide Calculator →
Download on the App StoreGet it on Google Play