Peptide BAC Water Calculator: Reconstitution and Dose
Calculate the exact BAC water volume to add, the insulin syringe units per dose, and how many doses your vial yields. Works for any lyophilized research peptide.
Quick presets
Click a peptide to load a typical vial size. The dose that loads with it is an arbitrary example value used only to demonstrate the arithmetic, not a typical or starting dose. Enter your own dose below.
Vial & dose inputs
How to reconstitute a peptide vial
Lyophilized peptides arrive as a freeze-dried powder. To use them, you mix the powder with bacteriostatic water (BAC) inside the sealed vial. Once reconstituted, the peptide is stable in the fridge for 30 to 60 days depending on the compound.
- Wipe both rubber stoppers (peptide vial and BAC vial) with an alcohol swab and let dry.
- Use a 1 mL or 3 mL syringe with a draw needle to pull the BAC water volume calculated above out of the BAC vial.
- Insert the needle into the peptide vial at a slight angle so the water runs down the inside wall, not directly onto the powder. This minimizes foaming.
- Inject slowly. Do not shake the vial. Gently swirl until fully dissolved.
- Label the vial with reconstitution date and concentration in mg/mL.
- Refrigerate. Do not freeze a reconstituted vial.
For detailed shipping and storage handling and what to do if the vial arrived warm, see the peptide legality guide and the supplier shipping notes on each city guide.
Picking the right BAC volume
The amount of BAC water you add does not change the total amount of peptide in the vial. It only changes the concentration, and therefore how much volume you draw per dose. Common choices:
1 mL of BAC water
Most concentrated option. Good for high-mass vials (10mg+) where dose volumes would otherwise be hard to read. Lasts the same number of weeks.
2 mL of BAC water
The most common default. Strikes a balance between syringe readability and concentration. Standard for most GLP-1 reconstitutions.
3 mL of BAC water
Diluted. Useful for small doses (under 200 mcg) where a more spread-out reading on the syringe reduces measurement error.
The math is identical regardless of volume. The only practical difference is how precise your syringe reading is. If you find yourself trying to read 1 to 2 units on the syringe, dilute more. If you are drawing close to syringe capacity, concentrate more.
Reading the insulin syringe
Almost everyone in the peptide world uses U-100 insulin syringes for reconstituted peptides. The conversion is:
1 unit = 0.01 mL
100 units = 1 mL = full 1 mL syringe
So 25 units on the syringe is 0.25 mL of solution. The calculator above does this conversion automatically. If you ever see a result like "0.083 mL," convert to units (8.3 units) for easier reading.
Smaller syringe sizes (0.3 mL and 0.5 mL) have finer graduations and are easier to read for small doses. The 1 mL syringe gives you headroom for higher-dose protocols like tirzepatide maintenance phases.
Common reconstitution mistakes
Confusing mg and mcg
The single most dangerous mistake. A 250 mcg dose is 1000x smaller than a 250 mg dose. Always confirm the unit on your protocol before drawing. The calculator labels units explicitly to reduce this risk.
Shaking the vial
Shaking creates foam, which destabilizes the peptide. Gentle swirling is correct. If the powder does not dissolve immediately, give it a minute and swirl again.
Reconstituting with sterile saline instead of BAC water
Bacteriostatic water contains benzyl alcohol, which prevents bacterial growth once the vial is punctured. Sterile saline does not. A peptide reconstituted with saline must be used within hours, not weeks.
Freezing a reconstituted vial
Freezing breaks the peptide structure. Lyophilized (dry) peptide can be frozen pre-reconstitution. Once water is added, refrigerate only.
Frequently asked questions
What is a BAC water calculator?
A BAC water calculator works out the concentration and dose volume that result from mixing a given amount of bacteriostatic water into a peptide vial. You enter the total peptide in the vial and how much BAC water you plan to add, and it returns the concentration in mg/mL, the volume per dose, and the equivalent insulin syringe units. It does the arithmetic only. It does not tell you what dose to take.
How much BAC water should I add to a 24mg retatrutide vial?
There is no single correct volume. BAC water volume is a readability choice, not a dosing choice: the total 24mg of peptide stays the same whether you add 1 mL, 2 mL, or 3 mL, only the concentration changes. Enter 24 as the vial amount in the calculator above and try a few BAC volumes to see how the concentration and syringe units shift, then match your protocol source's planned dose against that concentration.
How much BAC water for a 10mg or 20mg vial?
Same principle as any other vial size. A 10mg vial with 2 mL of BAC water gives a concentration of 5 mg/mL, and a 20mg vial with 2 mL gives 10 mg/mL. Enter your vial size above to see the exact concentration and how many insulin units a given dose from your protocol source works out to.
How many insulin units is 2mL of BAC water?
On a standard U-100 insulin syringe, 1 unit equals 0.01 mL, so 2 mL is 200 units, more than a single 1 mL syringe can hold. That figure describes the total BAC water added to the vial, not a single dose. A single dose is almost always a small fraction of that, and the calculator above converts your specific per-dose volume into units automatically.
Does adding more BAC water change the dose?
No. The total peptide mass in the vial is fixed at reconstitution and does not change no matter how much BAC water you add. Adding more water lowers the concentration, so you would draw a larger volume to reach the same dose. Adding less water raises the concentration, so the same dose is a smaller volume. The dose itself is set by your protocol source, not by the BAC water amount.
BAC water vs sterile water for reconstitution?
Bacteriostatic (BAC) water contains a small amount of benzyl alcohol as a preservative, which keeps a punctured, reconstituted vial usable for weeks in the fridge. Sterile water has no preservative, so a vial mixed with it should be used within hours, not weeks. For that reason BAC water is the standard choice for multi-dose peptide vials.
How many doses will my vial make?
Divide the total peptide in the vial by your per-dose amount. The calculator above does this automatically once you enter the vial size, BAC water volume, and dose, showing doses per vial alongside the concentration and syringe units. This is an arithmetic estimate assuming exact reconstitution, not a guarantee of vial yield.
How much BAC water for 100mg GHK-Cu?
The same concentration math applies regardless of compound. A 100mg GHK-Cu vial with 2 mL of BAC water works out to 50 mg/mL, or with 5 mL works out to 20 mg/mL. Enter 100 as the vial amount above and adjust the BAC water slider to see the resulting concentration and insulin units for your planned dose.
This is harm reduction education, not medical advice
This calculator is for educational use. Peptide protocols vary between individuals and compounds. Always cross-check with your protocol source, supplier instructions, and where possible a qualified clinician.