Peptide Reconstitution & Dose Calculator
How much bacteriostatic water to add, and exactly where to fill your syringe. Enter three numbers, get one clear answer and a picture of the fill line.
What reconstitution actually means
Peptides ship as a dry powder. That powder has been freeze-dried — the word you will see is lyophilised — because peptides are far more stable dry than wet. Reconstitution is simply the step where you add liquid and turn that powder back into something you can measure.
The liquid is normally bacteriostatic water: sterile water with a small amount of benzyl alcohol in it, which stops bacteria growing so the vial survives being punctured more than once.
Here is the part that confuses almost everybody. The vial label tells you how much peptide is inside. It does not tell you the concentration — because the concentration does not exist until you decide how much water to add. Two people with identical 10 mg vials can end up with strengths that differ by five times, purely because one added 1 mL and the other added 5 mL.
That is why there is no universal chart that says “draw to 10 units.” The number of units you draw depends on a choice you made a few minutes earlier. Get that relationship straight and the rest of this is just arithmetic.
How the calculator works
Three numbers in, one clear answer out — plus a syringe diagram showing where to stop.
Your vial
How many milligrams of peptide are in the vial, and how much bacteriostatic water you added. Both numbers matter equally.
Your dose
Your target dose in micrograms, and which syringe you are using — 1 mL, 0.5 mL or 0.3 mL. All are U-100.
Your fill line
The draw in units and in millilitres, with a drawn syringe showing exactly where the plunger stops.
The math, done once by hand
You do not need to do this yourself — that is what the tool is for. But seeing it once means you can sanity-check any answer, and catching a wrong answer matters more than getting a fast one.
There are only two facts to hold on to:
- 1 mg = 1,000 mcg. Vials are labelled in milligrams. Doses are usually discussed in micrograms. Almost every serious dosing error in this space lives in that gap.
- On a U-100 syringe, 100 units = 1 mL. So 1 unit is 0.01 mL. This is true of the 1 mL, 0.5 mL and 0.3 mL syringes alike — they just show a different number of lines.
Now change one thing. Same vial, same dose, but you added 1 mL of water instead of two. The concentration doubles to 10,000 mcg/mL, and the same 250 mcg dose becomes 2.5 units — half a line, on the most crowded part of the barrel.
Add 5 mL instead and it becomes 12.5 units. Still half a line, but on a much easier stretch of the syringe to read.
Same peptide. Same dose. Three completely different fill lines. Nothing about the drug changed — only your water.
Reconstitution reference chart
How many micrograms sit in one unit of a U-100 syringe, for common vial sizes and water volumes. Find your row, find your column, and you have your strength.
| Vial size | + 1 mL water | + 2 mL water | + 3 mL water | + 5 mL water |
|---|---|---|---|---|
| 2 mg | 20 mcg / unit | 10 mcg / unit | 6.7 mcg / unit | 4 mcg / unit |
| 5 mg | 50 mcg / unit | 25 mcg / unit | 16.7 mcg / unit | 10 mcg / unit |
| 10 mg | 100 mcg / unit | 50 mcg / unit | 33.3 mcg / unit | 20 mcg / unit |
| 15 mg | 150 mcg / unit | 75 mcg / unit | 50 mcg / unit | 30 mcg / unit |
| 20 mg | 200 mcg / unit | 100 mcg / unit | 66.7 mcg / unit | 40 mcg / unit |
| 30 mg | 300 mcg / unit | 150 mcg / unit | 100 mcg / unit | 60 mcg / unit |
To find your draw: divide your dose in micrograms by the number in the chart. A 300 mcg dose from a 10 mg vial reconstituted with 2 mL is 300 ÷ 50 = 6 units.
This chart converts between quantities. It is not a dosing recommendation, and it says nothing about what any particular compound should be used at or whether it suits you. Those are questions for a qualified healthcare professional who knows your history.
How much water should I add?
This is the most-asked question in reconstitution, and the honest answer surprises people: within reason, it is your choice, and there is no single right number.
The water does not change how much peptide you have. A 10 mg vial holds 10 mg whether you add 1 mL or 5 mL, and it will give you exactly the same number of doses either way. What the water changes is how easy your dose is to measure accurately.
Aim for a readable fill line
The practical target is a dose that lands somewhere around 5 to 30 units. Down at 2 or 3 units, a small wobble in the plunger is a large percentage error. Up near the top of the barrel you may not be able to fit the dose in one draw. In the middle, the lines are far enough apart to hit reliably.
Land on a whole line if you can
Whole numbers beat halves. In the worked example above, 2 mL of water put the dose on exactly 5 units. If a small change in your water volume moves you from 7.5 units to 8, take it — you will be drawing that line repeatedly, sometimes early in the morning, sometimes in poor light.
Respect the vial and the clock
Do not add more liquid than the vial comfortably holds. And remember that once a peptide is in solution its stable life is measured in weeks, not months — so there is no advantage in diluting a vial so far that you cannot finish it in time.
Write it on the vial. The date you mixed it and how much water you used. Future you will not remember, and a vial with no concentration written on it is a vial you cannot safely dose from.
How to reconstitute a vial, step by step
The arithmetic is one half of this. The physical handling is the other, and peptides are more fragile than most people expect.
- Let everything reach room temperature. Cold glass and cold liquid make the powder slower to dissolve and encourage you to rush it.
- Wipe both rubber stoppers with an alcohol swab — the peptide vial and the bacteriostatic water — and let them air dry rather than fanning or blowing on them.
- Draw your chosen volume of bacteriostatic water into a syringe. Use the calculator first so you know the number before the needle is in your hand.
- Aim at the glass, not the powder. Insert the needle at an angle so the stream runs down the inside wall of the vial. A jet fired straight into lyophilised powder can shear the peptide.
- Let it run in slowly. There is usually a slight vacuum in the vial that will draw the liquid in on its own; let it, rather than forcing the plunger.
- Swirl gently, or roll the vial between your palms. Most powders dissolve within a minute. Never shake. Shaking foams the solution and denatures peptide — the froth you see is damage.
- Wait until it is completely clear. If it stays cloudy, or you can see floating particles or stringy material after it has had time to settle, do not use it.
- Label the vial with the date and the concentration, then refrigerate it.
Bacteriostatic water and sterile water are not the same thing. Sterile water contains no preservative, so a vial mixed with it is intended to be used once and discarded. Bacteriostatic water contains benzyl alcohol, which is what allows a vial to be entered repeatedly over days or weeks.
Six mistakes worth knowing about
- Confusing mg with mcg. One milligram is a thousand micrograms. This single slip is the source of most thousand-fold errors, and it is why the calculator asks for the vial in mg and the dose in mcg — the units are kept apart on purpose.
- Treating “units” as a dose. Units measure volume, not peptide. “I take 10 units” means nothing to anyone else, because their vial is a different strength to yours.
- Assuming the label gives you the concentration. It gives you the quantity. The concentration is created by you, when you choose the water.
- Shaking the vial. Swirl or roll. Foam means denatured peptide, and no amount of waiting fixes it.
- Not recalculating after a change. New vial size, new water volume, new syringe — any of these changes your fill line. Run the numbers again rather than reusing last month’s.
- Reusing needles. A needle is blunted by its first pass through a rubber stopper, and a blunt needle does more tissue damage than a sharp one.
Common questions
Not to the amount of peptide you have, and not to the number of doses you get. It matters entirely to how easy your dose is to measure. Choose the volume that puts your dose on a clear, readable line.
It will dissolve the powder, but it has no preservative, so the vial should be used once and discarded rather than kept and re-entered. Bacteriostatic water is what makes a multi-use vial possible.
It means 100 units to the millilitre. A 1 mL, 0.5 mL and 0.3 mL syringe are all U-100 — they hold 100, 50 and 30 units respectively, but a unit means the same 0.01 mL on all three. Smaller barrels simply spread those units further apart, which makes small doses easier to read.
Check the answer against the reference chart above. Divide your dose by the mcg-per-unit figure for your vial and water volume, and see whether you get the same number the calculator gave you. If two independent routes agree, you are almost certainly fine.
It is workable but not ideal. Half-unit accuracy is hard to hit consistently, particularly low on the barrel. If it happens repeatedly, adjust the water volume on your next vial so the dose lands on a whole line.
Far less time than the powder does. Reconstituted peptides are generally refrigerated, protected from light, and used within a few weeks — but the window varies by compound. Check the specific compound rather than assuming a general rule.
Yes, and sometimes you should — particularly if your dose has changed and your current fill line has become awkward. Just recalculate before the first injection, and update the label.
Where to go next
The calculator handles one vial. These handle the rest.
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