Bac water calculator
The volume of bac water comes from your pharmacy’s instructions. This calculator shows the math behind it: enter your vial, your prescribed dose and a reading in units to see the matching volume, then check what any volume means in the table below.
How much water should I add?
Syringe
1 mL · 2-unit marks
The most liquid your vial holds, printed on the vial or box.
Add 2 mL of water. Each dose then reads 50 units.
Add this much bac water
2mL
- Strength
- 5 mg/mL
- Each unit holds
- 50 mcg
- Doses per vial
- 4
- whole doses
Show the math
Water to add
10 mg × 50 units ÷ (2.5 mg × 100) equals 2 mL
Strength this gives
2.5 mg × 100 ÷ 50 units equals 5 mg/mL
Check it forwards
2.5 mg ÷ 5 mg/mL × 100 equals 50 units
This is arithmetic, not medical advice. Confirm with your prescriber or pharmacist.
How our calculator worksCheck a water volume
The same vial with different amounts of water. Only the concentration changes, never the amount in the vial.
| Water | Strength | Each 2.5 mg dose |
|---|---|---|
| 0.5 mL | 20 mg/mL200 mcg per unit | 12.5 units0.125 mL |
| 1 mL | 10 mg/mL100 mcg per unit | 25 units0.25 mL |
| 1.5 mL | 6.667 mg/mL66.7 mcg per unit | 37.5 units0.375 mL |
| 2 mLYour answer | 5 mg/mL50 mcg per unit | 50 units0.5 mL |
| 2.5 mL | 4 mg/mL40 mcg per unit | 62.5 units0.625 mL |
| 3 mL | 3.333 mg/mL33.3 mcg per unit | 75 units0.75 mL |
| 5 mL | 2 mg/mL20 mcg per unit | 125 unitsOver 100 units |
How much bac water to add
Bacteriostatic water doesn’t change how much peptide is in the vial. It decides how concentrated the liquid is, and so how many units each dose takes up on the syringe. If your pharmacy gave you a volume, use it: check it in the table under the calculator.
Not sure what bac water is, or how it differs from sterile water? See bacteriostatic vs sterile water.
How a volume is worked out
Pharmacists work a volume out from the units each dose should read:
water mL = vial mg × units per dose ÷ (dose mg × 100)
For example, a 10 mg vial, a 2.5 mg dose and 50 units per dose: 10 × 50 ÷ (2.5 × 100) = 2 mL. Numbers for illustration only, not a dose. Use it to understand or check the volume on your instructions, not to replace it.
More water vs less water
- More water gives bigger unit numbers, which are easier to read and round less, but more liquid per injection.
- Less water gives a smaller draw. Under 2 units is hard to measure accurately, so the calculator flags it.
Any change to how you mix is one to confirm with your pharmacist first.
How much water a vial can hold
Keep to the volume printed on the vial, not the brim: a vial filled to the top leaves no room for the air you push in when you draw. Enter your vial size and every volume that won’t fit is marked. The vial capacity guide explains why.
Questions people ask
How much bacteriostatic water do I need for peptides?
There’s no single amount. The water sets the concentration, so the right volume is the one on your pharmacy’s instructions. If you weren’t given one, ask your pharmacist before mixing. The arithmetic pharmacists use is: water (mL) = vial mg × units per dose ÷ (dose mg × 100). A 10 mg vial, a 2.5 mg dose and 50 units per dose gives 2 mL (numbers for illustration only, not a dose).
How much bac water is 100 units?
On a U-100 insulin syringe, 100 units is exactly 1 mL, so 1 unit is 0.01 mL. That makes 2 mL of water 200 units, two full 100-unit syringes. Bac water is usually added with a separate mixing syringe; ask your pharmacist which one to use.
How much bac water for a 10 mg vial?
Use the volume on your pharmacy’s instructions. For reference, 1 mL makes 10 mg/mL (100 mcg per unit), 2 mL makes 5 mg/mL (50 mcg per unit) and 2.5 mL makes 4 mg/mL (40 mcg per unit). The amount in the vial stays 10 mg either way.
Can Peptinote tell me how many units to take?
No. Peptinote never suggests a dose. Enter the dose your prescriber gave you, and the calculator shows how to measure it: the units, the mL and where the line sits on your syringe, with every step of the math. If you aren’t sure what your dose is, ask your prescriber or pharmacist before drawing anything. How our calculator works.
Vial calculators
Pre-filled with the vial size. You add the water and the dose your prescriber gave you.
Related
Calculators
Guides
Every result is plain arithmetic from formulas we publish in full and check with automated tests. Peptinote doesn’t suggest doses and never sells or links to sellers of peptides.