What this does
Reconstitution is division. Divide the milligrams in the vial by the milliliters of water. That gives you concentration. Divide your dose by that concentration. That gives the volume to draw. Multiply that volume by 100 and you have the mark on an insulin syringe. This tool runs all three steps, draws the syringe, and shows the arithmetic.
What this tool is not. It converts milligrams into milliliters. It does not know what dose suits anything, because that is not an arithmetic question. For most research peptides there is no established human dose to look up. The tool assumes you already have a number and need the volume that matches it.
Calculators by compound
Same arithmetic, with the vial size already loaded and the trap specific to that compound written up beside it — the microgram gap on the secretagogues, the fixed ratio on the blends, the copper load on KLOW.
- Tesamorelin calculator
- BPC-157 calculator
- PT-141 calculator
- Sermorelin calculator
- BPC-157 TB-500 calculator
- CJC-1295 ipamorelin calculator
- TB-500 calculator
- KLOW calculator
Deliberately absent: the GLP-1s. “Retatrutide dosage calculator” is the largest single term in this cluster and it is not built here, for the reasons set out on retatrutide’s regulatory status.
How do you calculate a peptide dose?
Four lines of arithmetic. That is the whole method. Worth knowing them, if only to catch a calculator having a bad day.
| Step | Formula | Worked example |
|---|---|---|
| Concentration | mg in vial ÷ mL of water | 10 mg ÷ 2 mL = 5 mg/mL |
| Volume per dose | dose in mg ÷ concentration | 0.5 mg ÷ 5 mg/mL = 0.1 mL |
| Syringe units | volume in mL × 100 | 0.1 mL × 100 = 10 units |
| Strength per unit | concentration × 0.01 mL | 5 mg/mL × 0.01 = 50 mcg |
Units measure volume, not dose. This is the most common misreading in the whole area, and the most dangerous. An insulin syringe is graduated so 100 units = 1 mL. The mark tells you how much liquid you drew. It says nothing about how much peptide was dissolved in that liquid. Ten units of a 5 mg/mL solution is 0.5 mg. Ten units of a 1 mg/mL solution is 0.1 mg. Same mark, five-fold difference. Anyone who gives you a dose “in units” without stating the concentration has not given you a dose.
Peptide reconstitution calculator
Same tool, run backwards. Reconstitution asks a different question: not how much do I draw, but how much water should I add in the first place. That choice is yours, and it is the one decision on this page that you cannot undo. Once the water is in the vial, the concentration is set.
So the calculator answers it directly. Set your vial size and your dose, and the note under the results tells you which water volume would put that dose at a comfortable 20 units. Here is the same relationship as a table, for a 10 mg vial and a 0.5 mg dose.
| Water added | Concentration | 0.5 mg is | On the syringe |
|---|---|---|---|
| 1 mL | 10 mg/mL | 0.05 mL | 5 units |
| 2 mL | 5 mg/mL | 0.1 mL | 10 units |
| 3 mL | 3.33 mg/mL | 0.15 mL | 15 units |
| 4 mL | 2.5 mg/mL | 0.2 mL | 20 units |
| 5 mL | 2 mg/mL | 0.25 mL | 25 units |
The vial still holds 20 doses in every row. Water does not create or destroy peptide. It only changes how big each draw is. That is the single most useful thing to understand about reconstitution, and the table above is the proof.
How much bacteriostatic water should you add?
There is no correct answer, only a trade-off. Add more water and each dose becomes a larger volume that is easier to measure. Add less and the solution is stronger, but a dose can shrink below the smallest mark you can read.
A practical target is a draw between roughly 10 and 50 units. Below about 5 units, reading error becomes a large share of the dose. Past the capacity of your barrel you cannot draw the dose at all. The calculator flags both cases and suggests a water volume that clears them.
One thing the arithmetic will not tell you: which diluent to use. Bacteriostatic water carries 0.9% benzyl alcohol as a preservative, and that is what lets you enter a vial more than once. Sterile water has no preservative, so a vial mixed with it is single-use.
Which insulin syringe: 1 mL or 0.5 mL?
All three barrels below are U-100. That matters more than it sounds. A unit is 0.01 mL on every one of them, so the conversion never changes. What changes is how much the barrel holds and how finely it is printed.
| Syringe | Holds | Typical mark spacing | One unit is | Best for |
|---|---|---|---|---|
| 1 mL (100-unit) | 100 units | 2 units | 0.01 mL | Draws above about 20 units |
| 0.5 mL (50-unit) | 50 units | 1 unit | 0.01 mL | Draws of 10 to 50 units |
| 0.3 mL (30-unit) | 30 units | 1 unit | 0.01 mL | Small draws under 30 units |
A smaller barrel does not mean smaller units. It is the same unit, printed closer together, on a tube that holds fewer of them. Pick the smallest barrel your draw actually fits in, because that is the one with the finest printed marks. Change the syringe in the tool and the diagram redraws to that barrel, with its own scale and its own capacity warning.
Mark spacing varies by brand, so the tool never rounds your answer to it. It gives you the exact number of units, and tells you the nearest whole unit when the two differ. Whole units are numbered on every U-100 barrel, whatever the tick spacing.
Milligrams, micrograms and the 1,000× mistake
1 mg = 1,000 mcg. This is where the real damage happens. A vial is labeled in milligrams. Plenty of write-ups are in micrograms. Slipping a factor of a thousand between the two is the easiest mistake to make here, and the worst.
So the tool asks for the unit rather than inferring it. It also converts your dose when you switch units, instead of reusing the digits. Picking “mcg” will never silently turn 0.5 mg into 0.5 mcg. Both figures appear in the results for the same reason.
What this calculator cannot tell you
The arithmetic is the easy part. These are the parts that actually decide whether a reconstituted vial is any good:
- Technique. Water runs down the vial wall rather than jetting onto the powder. The vial gets swirled, not shaken. Both rules come down to shear and the air-liquid interface.
- Stability after mixing. A lyophilized peptide keeps for a long time. The same peptide in solution is on a clock. Storage and stability covers what that clock depends on.
- How the dose gets delivered. Route changes absorption, and it is why every reconstitution figure ends in syringe units. Injection routes explained.
- Whether the vial holds what the label says. No calculator can tell you that. A batch-matched certificate of analysis can, and who publishes one is the question underneath every number on this page.
What vial size will you actually be reconstituting?
Check it on the product page, not on the write-up you took the dose from. Vial size is the first input on this page, and it is the one people carry over from somewhere else. Seven of the ten retailers below sell BPC-157 as a 5 mg vial. Two sell 10 mg. Put a 10 mg vial into the tool when you are holding a 5 mg one and every number it returns is out by half.
Prices are per vial as listed on 2026-08-13, with the per-milligram figure beside them so different vial sizes can be compared at all. Disclosure: Where To Buy Peptides earns a commission on purchases made through its links.
| Vendor | BPC-157 vial | $/mg | Ships free at | Where the COA lab is named |
|---|---|---|---|---|
| Sports Technology Labs | 5 mg $56.99 | 11.40 | $149 | Site and document |
| Swiss Chems | 5 mg $39.99‡ | 8.00‡ | $100 | Site (FAQ) |
| Core Peptides | 5 mg $52.00 | 10.40 | $200 | Document only |
| PS Peptides | 5 mg $49.99 | 10.00 | $200 | Document only |
| BioTech Peptides | 5 mg $52.00 | 10.40 | $200 | Document only |
| American Peptides | 5 mg $60.00 | 12.00 | $300 | Document only |
| Limitless Biotech | Price gated | — | None | Neither |
| Behemoth Labz | 5 mg $62.27 | 12.45 | $100 | Document only |
| Red Rock Peptides | 10 mg $69.00† | 6.90† | Not offered | None published |
† 10 mg vial, so the per-milligram figure is not directly comparable with a 5 mg row. ‡ Swiss Chems sells the arginine salt rather than plain BPC-157, and the price shown is a sale price; the list price works out at $10.00/mg.
The last column is the one worth reading twice. Eight of the ten publish a real third-party certificate; only three name the testing lab in their own site copy, and one publishes nothing while claiming otherwise. How to read a certificate of analysis covers what to check once you have the document open.
Frequently asked questions
How do you calculate peptide reconstitution?
Divide the milligrams of peptide in the vial by the milliliters of bacteriostatic water you add. That gives the concentration in mg/mL. Then divide your dose by that concentration. That gives the volume to draw. A 10 mg vial with 2 mL of water is 5 mg/mL, so a 0.5 mg dose is 0.1 mL.
How many units is 0.1 mL on an insulin syringe?
10 units. Insulin syringes are U-100, which means 100 units equals 1 mL and one unit equals 0.01 mL. So units are just milliliters times 100. That marking measures volume, not dose. Ten units of a 5 mg/mL solution and ten units of a 2 mg/mL solution hold very different amounts of peptide.
How much bacteriostatic water should I add to a 10 mg vial?
There is no single right answer. It is a trade-off you choose. More water makes each dose a bigger volume that is easier to read. Less water makes the solution stronger, so a dose can fall below the smallest mark on the syringe. Many people pick a volume that puts their dose between 10 and 50 units.
What is the difference between a 1 mL and a 0.5 mL insulin syringe?
Capacity and mark spacing, not the size of a unit. Both are U-100, so one unit is 0.01 mL on either. The 1 mL barrel holds 100 units and is usually printed every 2 units. The 0.5 mL barrel holds 50 units and is usually printed every 1 unit, so small draws are easier to read on it.
What is the difference between mcg and mg?
1 mg equals 1,000 mcg. Slipping a factor of a thousand is the most common arithmetic mistake in this whole area. Vials are labeled in milligrams, and plenty of write-ups are written in micrograms. The calculator asks for the unit rather than guessing it, and it converts the number when you switch.
Does the peptide powder add to the volume?
Not enough to matter. A few milligrams of lyophilized powder displaces far too little volume to register against 1 to 3 mL of water. The calculation treats total volume as the water volume. That assumption is standard, and the error is much smaller than syringe reading error.
How do I know how many doses are in a vial?
Divide the milligrams in the vial by your dose in milligrams. The water volume does not change that number. A 10 mg vial holds 20 doses of 0.5 mg whether you reconstitute it with 1 mL or with 3 mL. Water changes the volume of each draw, not the amount of peptide in the vial.
What happens if I add too much bacteriostatic water?
Nothing is lost. The arithmetic just changes. The same milligrams sit in more liquid, so the solution is weaker and every draw is a larger volume. The risk is that the draw grows past the capacity of your syringe. The vial still holds the same number of doses.
Can I use sterile water instead of bacteriostatic water?
Only for a vial you will enter once. Bacteriostatic water carries 0.9% benzyl alcohol, which suppresses microbial growth. That preservative is what makes repeat entry into a vial reasonable. Sterile water has none, so a vial reconstituted with it is single-use.
How long does a reconstituted peptide last?
Far less time than the powder did. Refrigerated at 2 to 8 degrees Celsius and kept out of light, peptides in solution are commonly treated as usable for a few weeks. The honest answer is sequence-dependent. Methionine and cysteine residues oxidize, and asparagine and glutamine deamidate.
How do you calculate a dose for a blend?
Treat each compound on its own. A blend vial lists milligrams per compound, and one draw delivers all of them at a fixed ratio. Run the calculation on the compound you are targeting, then run the same volume against the other compound to see what it delivers.
References
- American Society of Health-System Pharmacists (ASHP). Handbook on Injectable Drugs: Benzyl alcohol preservative compatibility and stability data. https://www.ashp.org/products-and-services/database-tools/handbook-on-injectable-drugs
- United States Pharmacopeia. (2024). Bacteriostatic Water for Injection — monograph and in-use stability guidance. USP-NF. (See institutional access.) https://doi.org/10.4135/9781412963855.n1200
- Wang, W. (1999). Instability, stabilization, and formulation of liquid protein pharmaceuticals. International Journal of Pharmaceutics, 185(2), 129–188. https://doi.org/10.1016/s0378-5173(99)00152-0
The arithmetic needs no citation; the diluent and stability guidance does.