Peptide Reconstitution Calculator & Concentration Chart
How much bacteriostatic water to add to a peptide vial, how to work out the concentration, a U-100 unit conversion chart and step-by-step reconstitution.
Skip the maths: use the calculator
Pick your vial, enter the water, and read off the units to draw.
Reconstitution is where most handling mistakes happen. Not in storage, not in transport, but in the two minutes where someone adds water to a vial and then has to know exactly what concentration they have made.
The good news is that the whole thing reduces to one formula. Learn it once and it applies to every lyophilised peptide, from BPC-157 to retatrutide.
This guide covers the maths, the procedure, a concentration chart and a unit conversion chart, plus notes on specific compounds and on storage.
Important: This guide explains reconstitution and concentration only. It does not give dosing advice. All STRIATA products are sold strictly for research purposes and are not intended for human or veterinary use.
What is reconstitution?
Peptides are supplied as a lyophilised (freeze-dried) powder in a sterile, sealed vial. Reconstitution is the process of dissolving that powder in a suitable solvent to produce a solution of a known concentration.
The solvent is almost always bacteriostatic water (BAC water), which contains 0.9% benzyl alcohol as a preservative. That preservative is what allows a reconstituted vial to remain usable for up to 30 days at 2–8 °C.
Sterile water for injection (SWFI) contains no preservative. A vial reconstituted with sterile water should be used within 24 hours. For any vial that will be drawn from more than once, BAC water is the correct choice.
Equipment you need
| Item | Notes |
|---|---|
| Bacteriostatic water | 0.9% benzyl alcohol; the preferred solvent for multi-use vials |
| Insulin syringe (U-100) | 1 mL, marked in 100 units; the standard for measuring small volumes |
| Larger draw syringe | Optional; 3–5 mL for drawing BAC water into the peptide vial |
| Alcohol swabs (70% IPA) | Wipe vial tops before every single needle insertion |
| Refrigerator (2–8 °C) | For storage after reconstitution; never freeze reconstituted solution |
| Sharps container | Biohazard sharps bin; never recap needles |
The master formula
Everything in reconstitution comes down to this:
Concentration (mg/mL) = Peptide mass (mg) ÷ BAC water added (mL)
From that, two derived forms answer every other question:
Peptide in a given volume (mg) = Concentration (mg/mL) × Volume (mL)
Volume (mL) = Units on a U-100 syringe ÷ 100
Understanding the U-100 syringe
A U-100 insulin syringe holds 1 mL in total. The barrel is graduated into 100 equal units, so each unit equals 0.01 mL. Once that clicks, the conversions stop being confusing.
| Syringe mark | Volume | Fraction of 1 mL |
|---|---|---|
| 10 units | 0.10 mL | One tenth |
| 20 units | 0.20 mL | One fifth |
| 25 units | 0.25 mL | One quarter |
| 50 units | 0.50 mL | One half |
| 100 units | 1.00 mL | Full syringe |
Concentration reference chart
The resulting concentration for common vial sizes and BAC water volumes, and how much peptide each unit on a U-100 syringe contains at that concentration.
| Vial size | BAC water added | Concentration | Per unit on U-100 |
|---|---|---|---|
| 1 mg | 1.0 mL | 1.0 mg/mL | 10 mcg |
| 1 mg | 2.0 mL | 0.5 mg/mL | 5 mcg |
| 2 mg | 1.0 mL | 2.0 mg/mL | 20 mcg |
| 2 mg | 2.0 mL | 1.0 mg/mL | 10 mcg |
| 5 mg | 1.0 mL | 5.0 mg/mL | 50 mcg |
| 5 mg | 2.0 mL | 2.5 mg/mL | 25 mcg |
| 5 mg | 5.0 mL | 1.0 mg/mL | 10 mcg |
| 10 mg | 1.0 mL | 10.0 mg/mL | 100 mcg |
| 10 mg | 2.0 mL | 5.0 mg/mL | 50 mcg |
| 10 mg | 5.0 mL | 2.0 mg/mL | 20 mcg |
| 10 mg | 10.0 mL | 1.0 mg/mL | 10 mcg |
Practical tip: a lower concentration (more water) spreads the same amount of peptide over a larger volume, which makes small amounts easier to measure accurately. A higher concentration keeps volumes small. Neither is better for stability; it is purely a question of what is easiest to measure.
Unit conversion chart
How much peptide a given number of units contains at each concentration.
| Units ↓ / Conc → | 0.5 mg/mL | 1.0 mg/mL | 2.0 mg/mL | 2.5 mg/mL | 5.0 mg/mL | 10.0 mg/mL |
|---|---|---|---|---|---|---|
| 5 U (0.05 mL) | 25 mcg | 50 mcg | 100 mcg | 125 mcg | 250 mcg | 500 mcg |
| 10 U (0.10 mL) | 50 mcg | 100 mcg | 200 mcg | 250 mcg | 500 mcg | 1 mg |
| 20 U (0.20 mL) | 100 mcg | 200 mcg | 400 mcg | 500 mcg | 1 mg | 2 mg |
| 25 U (0.25 mL) | 125 mcg | 250 mcg | 500 mcg | 625 mcg | 1.25 mg | 2.5 mg |
| 50 U (0.50 mL) | 250 mcg | 500 mcg | 1 mg | 1.25 mg | 2.5 mg | 5 mg |
| 100 U (1.00 mL) | 500 mcg | 1 mg | 2 mg | 2.5 mg | 5 mg | 10 mg |
The reconstitution calculator does the same arithmetic for any vial in the catalogue and any water volume.
Step-by-step reconstitution procedure
1. Wash your hands thoroughly and work on a clean, flat surface.
2. Remove both vials from refrigeration and allow the peptide vial and the BAC water to reach room temperature, around 5–10 minutes. This reduces the risk of thermal shock to the peptide.
3. Swab the rubber septum of both vials with a fresh 70% IPA swab. Allow 10 seconds to air-dry before inserting any needle.
4. Draw your chosen volume of BAC water into the syringe. For example, 1 mL to make 1 mg/mL from a 1 mg vial, or 2 mL to make 5 mg/mL from a 10 mg vial.
5. Insert the needle into the peptide vial at an angle so that the stream of water runs down the inside wall of the vial rather than landing directly on the powder cake. This prevents foaming and protects the peptide from degradation.
6. Do not shake. Gently roll the vial between your palms or swirl it slowly until the powder is fully dissolved. Most peptides dissolve within 30–60 seconds; some, notably TB-500, take one to two minutes.
7. Inspect the solution visually. It should be clear and colourless, or very faintly yellow for some compounds. Discard if cloudy, particulate or discoloured.
8. Label the vial immediately with the compound name, concentration in mg/mL, the date reconstituted, and your initials. Store at 2–8 °C.
Never use ultrasonic baths, vortex mixers, or vigorous shaking. Peptide bonds are fragile and mechanical stress degrades potency. Gentle swirling only.
Worked concentration examples
Example A: BPC-157, 5 mg vial
BAC water added: 2.0 mL.
- Concentration = 5 mg ÷ 2.0 mL = 2.5 mg/mL
- Each unit = 0.01 mL × 2.5 mg/mL = 25 mcg
- 10 units (0.10 mL) contain 250 mcg
Example B: GHK-Cu, 5 mg vial
BAC water added: 5.0 mL.
- Concentration = 5 ÷ 5.0 = 1.0 mg/mL
- Each unit = 10 mcg
- A full 1 mL syringe contains 1 mg
Example C: Semaglutide, 2 mg vial, and an awkward number
BAC water added: 1.0 mL gives 2.0 mg/mL, where 0.25 mg sits at 12.5 units, between two marks.
Better approach: reconstitute in 2 mL instead, giving 1.0 mg/mL, and 0.25 mg sits on the 25-unit mark. Same amount, far easier to measure. This is exactly the situation where adding more water solves the problem.
Example D: TB-500, 5 mg vial
BAC water added: 1.0 mL.
- Concentration = 5 ÷ 1.0 = 5.0 mg/mL
- Each unit = 50 mcg
TB-500 needs a longer dissolution time: one to two minutes of gentle swirling.
Compound-specific reconstitution notes
| Compound | Vial | BAC water | Concentration | Notes |
|---|---|---|---|---|
| BPC-157 | 5 mg | 2 mL | 2.5 mg/mL | Dissolves readily, clear solution. Light-sensitive; store in an amber vial or wrap in foil. |
| TB-500 | 5 mg | 1–2 mL | 2.5–5 mg/mL | Slow to dissolve; allow 2–3 minutes of gentle swirling. May look slightly viscous initially. |
| GHK-Cu | 5 mg | 5 mL | 1 mg/mL | A blue-green tint is normal; it is a copper chelate. Avoid contact with vitamin C or citric acid, which displaces the copper. |
| CJC-1295 No-DAC | 2 mg | 2 mL | 1 mg/mL | Stable in BAC water; use within 28 days. |
| Ipamorelin | 2 mg | 2 mL | 1 mg/mL | Clear solution. |
| Semaglutide | 2 mg | 1–2 mL | 1–2 mg/mL | 2 mL gives 1 mg/mL, the easiest concentration to measure from. |
| Tirzepatide | 5 mg | 1–2 mL | 2.5–5 mg/mL | Dissolves readily. |
| Retatrutide | 5 mg | 2 mL | 2.5 mg/mL | Handle as for tirzepatide. Long-term stability data is limited; use within 21 days. |
| KPV | 50 mg | 10 mL | 5 mg/mL | Very water-soluble and extremely stable once reconstituted. |
Storage and stability after reconstitution
| State | Storage temperature | Shelf life | Notes |
|---|---|---|---|
| Lyophilised powder, sealed | Room temperature (15–25 °C) | To expiry date, typically 24+ months | Keep away from direct light and moisture |
| Lyophilised powder, unsealed | 2–8 °C refrigerated | Within 6 months | Do not freeze |
| Reconstituted in BAC water | 2–8 °C refrigerated | 28–30 days | Do not freeze; discard if cloudy |
| Reconstituted in sterile water | 2–8 °C refrigerated | Within 24 hours | Prepare only what you need immediately |
| Reconstituted, frozen in aliquots | −20 °C | Up to 3 months | Single freeze only; never refreeze after thawing |
Never boil, autoclave, or expose reconstituted peptide solutions to temperatures above 37 °C. Heat permanently denatures peptide structure and cannot be undone.
Store reconstituted vials at the back of the fridge, not in the door. The door experiences a temperature spike every time the fridge is opened, and for GLP-1 class peptides in particular, that cycling meaningfully shortens usable life.
Troubleshooting
| Issue | What to do |
|---|---|
| Powder won't dissolve | Allow more time and gently swirl or roll the vial. Some peptides, particularly TB-500, need 2–3 minutes. Never shake. |
| Cloudy solution | Do not use. May indicate contamination, precipitation, or degraded peptide. Discard. |
| Floating particles | Discard. Could be peptide aggregates or particulate contamination; neither can be filtered out. |
| Blue or green tint | Normal for GHK-Cu due to the copper content. Other peptides should be clear to faintly yellow. |
| Foamy solution | Caused by adding BAC water directly onto the powder. Discard if severely foamed; otherwise wait about 10 minutes for bubbles to settle. |
| Unsure of concentration | Discard and reconstitute fresh. Never estimate; always recalculate from the formula. |
| Air bubble in syringe | Tap the barrel gently and push the bubble out before reading the volume, or the measurement will be short. |
Frequently asked questions
How much BAC water should I add to my peptide vial?
There is no single correct answer. The amount of water only sets the concentration, and any volume from 1 to 3 mL is fine from a stability standpoint for most vials (glutathione and NAD+ need up to 10 mL). Pick the volume that gives a concentration that is easy to measure from, which usually means a round number such as 1, 2, 2.5 or 5 mg/mL.
Can I use sterile water instead of bacteriostatic water?
Only if the entire vial will be used within 24 hours. Sterile water has no preservative, so any multi-use vial reconstituted with it becomes a contamination risk. For anything drawn from more than once, use BAC water.
What happens if I shake the vial?
Shaking triggers fibrillar aggregation: the peptide chains clump together and the compound loses activity. This is irreversible. Once a peptide has aggregated, no amount of mixing, warming or filtering will restore it. Gentle swirling only.
How long does a reconstituted peptide last?
Generally 28–30 days refrigerated in BAC water, though this varies by compound. GLP-1 class peptides such as tirzepatide and semaglutide sit at the shorter end of that window, and retatrutide should be used within 21 days given limited stability data. More robust compounds like BPC-157 and TB-500 tolerate longer. Label every vial with its reconstitution date so you are never guessing.
Can I freeze a reconstituted vial?
Not in a normal fridge-freezer for routine use. Ice crystal formation disrupts peptide structure. Pre-aliquoted solution stored at −20 °C can hold for up to three months, but only as a single freeze; never refreeze after thawing.
How do I work out how much peptide is in a given volume?
Multiply the concentration in mg/mL by the volume in mL. On a U-100 syringe, the volume in mL is the number of units divided by 100. So 20 units of a 2.5 mg/mL solution is 0.2 mL × 2.5 mg/mL = 0.5 mg. The unit conversion chart above covers the most common combinations.
My vial has gone cloudy before the expiry window. What now?
Discard it and do not use it. Then consider the cause: cloudiness well inside the shelf life, with correct storage, may indicate a product quality issue rather than handling error. If you bought from STRIATA, get in touch: describe what you are seeing and when you reconstituted it, and we will work out what happened.
Questions about a specific compound?
If you are unsure about a reconstitution volume, a concentration calculation, or whether a vial is still good to use, message us. We would rather answer a question than have someone guess.
Website: striatalabs.co.za
Email: info@striatalabs.co.za
WhatsApp: +27 78 213 7905
Sources
The research, regulatory documents and clinical guidelines behind the claims in this article:
- US National Library of Medicine, DailyMed. Bacteriostatic Water for Injection USP, prescribing information (0.9% benzyl alcohol as preservative). DailyMed.
- Manning MC, Chou DK, et al. Stability of protein pharmaceuticals: an update. Pharmaceutical Research, 2010.
- D'Hondt M, Bracke N, et al. Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis, 2014.
- Fosgerau K, Hoffmann T. Peptide therapeutics: current status and future directions. Drug Discovery Today, 2015.
This guide is produced by STRIATA for educational purposes and does not constitute medical advice. All products are sold strictly for research purposes only. Not intended for human or veterinary use. Not approved by SAHPRA for human consumption.
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