Bacteriostatic Water and Mixing Math
Peptide mixing math comes down to one formula: concentration = peptide amount divided by diluent volume. This educational guide shows how to choose a bacteriostatic water volume and convert it into insulin-syringe units with worked examples. It is not medical advice.
Peptide mixing math comes down to one idea: concentration = peptide amount ÷ diluent volume. Once you know the concentration, converting to insulin-syringe units is simple arithmetic. This guide explains bacteriostatic water and walks through worked examples, for educational purposes only. It is not medical advice, and the numbers below are illustrative math, not dosing recommendations.
What is bacteriostatic water?#
Bacteriostatic water is sterile water for injection containing about 0.9% benzyl alcohol, a preservative that inhibits bacterial growth. That preservative is the reason it is commonly chosen for multi-use vials accessed repeatedly over days or weeks, whereas plain sterile water has no antibacterial protection. It is a pharmaceutical product — household or distilled water is never a substitute.
What is the one formula you need?#
The whole of peptide mixing math rests on a single relationship:
Concentration = total peptide amount ÷ volume of diluent added
Everything else — per-mL concentration, per-unit concentration, and how many units to draw — flows from this. The only other things you need are two unit facts: 1 mg = 1,000 mcg, and on a U-100 insulin syringe, 1 mL = 100 units (so 1 unit = 0.01 mL).
How do you calculate concentration, step by step?#
The short answer: convert mg to mcg, divide by your water volume to get mcg/mL, then divide by 100 to get mcg per unit. Here is a fully worked example using a 5 mg vial reconstituted with 2 mL of bacteriostatic water:
- Convert to micrograms: 5 mg × 1,000 = 5,000 mcg total in the vial.
- Per-mL concentration: 5,000 mcg ÷ 2 mL = 2,500 mcg/mL.
- Per-unit concentration: 2,500 mcg/mL ÷ 100 units/mL = 25 mcg per unit.
- Draw a desired amount: to measure 250 mcg, divide by per-unit concentration: 250 ÷ 25 = 10 units on a U-100 syringe.
How does the water volume change the math?#
More water spreads the same peptide across more volume, so each unit holds less peptide — which makes small amounts easier to fine-tune. Less water concentrates it, so each unit holds more. The table below shows the same 5 mg vial reconstituted with different volumes of bacteriostatic water:
| Water added | Concentration (per mL) | Concentration (per unit, U-100) | Units to draw 250 mcg |
|---|---|---|---|
| 1 mL | 5,000 mcg/mL | 50 mcg/unit | 5 units |
| 2 mL | 2,500 mcg/mL | 25 mcg/unit | 10 units |
| 2.5 mL | 2,000 mcg/mL | 20 mcg/unit | 12.5 units |
| 5 mL | 1,000 mcg/mL | 10 mcg/unit | 25 units |
Notice the total peptide never changes — only how it is distributed. Choosing a volume that lands your typical measurement on an easy-to-read number of units reduces error.
A second worked example#
For a 10 mg vial reconstituted with 2 mL:
- 10 mg × 1,000 = 10,000 mcg total.
- 10,000 ÷ 2 = 5,000 mcg/mL.
- 5,000 ÷ 100 = 50 mcg per unit.
- To measure 100 mcg: 100 ÷ 50 = 2 units.
The procedure is identical regardless of vial size — only the input numbers change.
Why convert milligrams to micrograms?#
Vials are usually labeled in milligrams, but amounts are often discussed in micrograms, and converting early (1 mg = 1,000 mcg) keeps the per-unit numbers whole and manageable. Working in mixed units is where decimal-point mistakes creep in, and a misplaced decimal is a serious error.
A note on safety#
These calculations describe volume and concentration only — they say nothing about what amount, if any, is appropriate for a person. Each vial access carries contamination risk, benzyl alcohol is not suitable for everyone (for example, it is generally avoided in neonates), and product labeling and a clinician's guidance always take precedence. WikiPeps teaches the math so the community can read a label correctly, not to recommend a dose.
The bottom line#
Peptide mixing math is one formula: concentration = peptide amount ÷ diluent volume. Convert mg to mcg, divide by your water volume for mcg/mL, divide by 100 for mcg per unit, then divide your desired amount by that to get units on a U-100 syringe. Label everything, double-check decimals, and consult a licensed clinician before any health decision.
How to calculate peptide concentration and syringe units (educational overview)
What you'll need
- Peptide vial labeled with total mg
- Bacteriostatic water
- U-100 insulin syringe
- Calculator and a pen for labeling
Read the total peptide amount
Find the total milligrams printed on the vial (for example, 5 mg) and convert to micrograms: 5 mg x 1,000 = 5,000 mcg.
Choose your diluent volume
Pick a bacteriostatic water volume that makes the math clean, such as 1 mL or 2 mL. This volume sets your concentration.
Calculate concentration per mL
Divide total mcg by mL of water. Example: 5,000 mcg / 2 mL = 2,500 mcg per mL.
Convert to per-unit concentration
Divide the per-mL concentration by 100 (since 100 units = 1 mL on U-100). Example: 2,500 / 100 = 25 mcg per unit.
Convert a desired amount to units
Divide your desired mcg by mcg-per-unit. Example: to draw 250 mcg at 25 mcg/unit, 250 / 25 = 10 units.
Label the vial with everything
Write the peptide name, total amount, water added, resulting concentration (mcg/unit), and date on the vial so you never have to recalculate from memory.
Frequently asked questions
What is bacteriostatic water?
- Bacteriostatic water is sterile water for injection that contains about 0.9% benzyl alcohol, a preservative that inhibits bacterial growth. That preservative is why it is commonly chosen for multi-use vials that are accessed repeatedly over days or weeks.
How do you calculate peptide concentration?
- Concentration equals the total peptide amount divided by the volume of diluent added. For example, 5 mg of peptide dissolved in 2 mL of bacteriostatic water gives 2.5 mg/mL, which is 2,500 mcg/mL, or 25 mcg per unit on a U-100 insulin syringe.
How much bacteriostatic water should I add to a peptide vial?
- There is no single right answer — more water makes each unit hold less peptide (easier to fine-tune small amounts), while less water concentrates it. Many people pick a round volume like 1 mL or 2 mL so the per-unit math is clean. The decision should follow product guidance and a clinician's advice.
How do I convert a desired peptide amount into syringe units?
- Divide your desired peptide amount (in mcg) by the concentration per unit (in mcg per unit). If your solution is 25 mcg per unit and you want 250 mcg, that is 250 / 25 = 10 units on a U-100 syringe.
Why convert milligrams to micrograms in peptide math?
- Peptide vials are usually labeled in milligrams (mg), but doses are often discussed in micrograms (mcg). Since 1 mg = 1,000 mcg, converting to mcg keeps the per-unit numbers manageable and reduces decimal-point errors.
Can I reuse the same bacteriostatic water vial for different peptides?
- Each access of a vial introduces contamination risk, and cross-using supplies compounds it. Follow sterile technique, keep separate clearly labeled vials, and follow product labeling. When in doubt, consult a pharmacist or clinician.
References
- 1.Bacteriostatic Water for Injection, USP — composition and labeling — U.S. Pharmacopeia / manufacturer labeling · 2023
- 2.Benzyl alcohol as a pharmaceutical preservative (safety review) — Peer-reviewed pharmaceutical literature (PubMed-indexed) · 2018
- 3.Safe Injection Practices — U.S. Centers for Disease Control and Prevention (CDC) · 2024