Tools / Bac water planner
How much bac water to add
Before you mix, pick a water amount that puts your dose exactly on a line of your syringe. Round lines like 10 or 20 are the easiest to read.
Example: a 5 mg vial and a 250 mcg dose. Add 2 mL and each dose is the 10-unit line.
The mg printed on the vial label.
Check whether it says mcg or mg. They differ by 1,000 times.
It's printed on the packet: 0.3, 0.5 or 1 mL.
Check how much room your vial has before you add water.
Add this much water
2mL
Then each 250 mcg dose is the 10 line on a 1 mL syringe.
Other amounts that land on a line
- Strength after mixing
- 2.5 mg/mL
- Each unit holds
- 25 mcg
- Doses in this vial
- 20
Round numbers like 10 or 20 units are the easiest lines to read. Check your vial has room for the water before you add it.
Checked 8 November 2026 by the PeptideTracker editorial team · This tool does the math only. It doesn't recommend a dose.
[02] Quick answers
Water that lands on a round line (1 mL syringe)
The first water amount, up to 3 mL, that puts each dose on a multiple of 10 units on a 1 mL syringe.
| Vial | 100 mcg dose | 250 mcg dose | 500 mcg dose | 1,000 mcg dose |
|---|---|---|---|---|
| 5 mg | none | 2 mL → 10 | 1 mL → 10 | 0.5 mL → 10 |
| 10 mg | none | none | 2 mL → 10 | 1 mL → 10 |
| 15 mg | none | none | 3 mL → 10 | 1.5 mL → 10 |
| 20 mg | none | none | none | 2 mL → 10 |
[03] How it works
Why the water amount matters
The water doesn't change how much peptide is in the vial. It changes how much each unit on the syringe holds. More water means each unit holds less, so the same dose takes more units.
Most 1 mL syringes have a line every 2 units (some brands mark every unit). If your dose works out to 15 units, it falls between lines. The planner only shows amounts that land exactly on a line.
[04] Questions
Questions
How much bacteriostatic water do I add to a 5 mg vial?
Any amount works for the math, but some make measuring easier. For a 250 mcg dose, 2 mL of water puts each dose on the 10-unit line of a 1 mL syringe. For a 500 mcg dose, 2 mL puts it on the 20-unit line.
Does more water make the peptide weaker?
It makes each unit hold less, but the total in the vial stays the same. You draw more units for the same dose. Small doses become easier to measure.
Can I add water after I've already mixed the vial?
Yes, but it changes every dose after it, and you can't take water out. Run the reconstitution calculator with the total water you added.
What is bacteriostatic water?
Sterile water with 0.9% benzyl alcohol, which slows bacterial growth so a vial can be used for more than one dose. Plain sterile water has no preservative.
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[05] Read next
Guides that go with this calculator
- How much bac water to add to a peptide vialThere's no single right amount. The water sets how much peptide each unit on your syringe holds, so choose an amount that puts your dose on a line you can read.
- How to reconstitute peptidesMixing (reconstituting) means adding bacteriostatic (bac) water to the freeze-dried powder in your vial so you can measure out doses. How much water you add, and how you add it, sets every dose that follows.
- How long do reconstituted peptides last?Nobody has published tested numbers for research peptides once they're mixed. Approved peptides and GLP-1 pens do have exact label limits, and they vary a lot from product to product.
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