How Much BAC Water to Reconstitute Peptides
The amount of bacteriostatic water you add decides your concentration — and therefore how many syringe units each dose is. There's no single right answer, but there are sensible defaults. Here's how to choose.
The short answer
- 5 mg vial: 1–2 mL of BAC water is the common range
- 10 mg vial: 2 mL is the most common choice
The goal is a concentration where your typical dose lands between roughly 5 and 50 units on a 1 mL (100-unit) insulin syringe — easy to measure accurately, comfortable to inject.
Concentration cheat sheet
| Vial size | BAC water | Concentration | 250 mcg dose = |
|---|---|---|---|
| 5 mg | 1 mL | 5,000 mcg/mL | 5 units |
| 5 mg | 2 mL | 2,500 mcg/mL | 10 units |
| 10 mg | 1 mL | 10,000 mcg/mL | 2.5 units |
| 10 mg | 2 mL | 5,000 mcg/mL | 5 units |
The formula for any dose
units to draw = (dose in mcg ÷ concentration in mcg/mL) × 100
Example: 10 mg vial + 2 mL water = 5,000 mcg/mL. A 500 mcg dose is (500 ÷ 5,000) × 100 = 10 units.
LogMyPeptides does this automatically — enter your vial size and water volume once per vial, and every log entry shows the exact units to draw. The built-in converter also handles mg, mcg and IU.
More water vs. less water
- More water (lower concentration): bigger, easier-to-read draws; better for small doses like 100–250 mcg. Downside: larger injection volumes and the vial runs out faster per draw.
- Less water (higher concentration): tiny injection volumes; better for large doses like 2–5 mg. Downside: measuring errors are amplified — one unit off is a bigger percentage of your dose.
Practical tips
- Write the water volume and date on the vial as soon as you mix it — you'll forget otherwise
- Aim the stream at the vial wall and swirl gently; never shake (full technique in our reconstitution guide)
- Refrigerate after mixing and use within the supplier's stated window
- If you switch water volumes between vials of the same peptide, update your log — the same "10 units" is a different dose at a different concentration