Reconstitution calculator
Say what's in the vial and what each draw should contain. It shows what the draw works out to for each common amount of liquid, and marks the one that's easiest to measure.
What this does: works out how much bac water to add, and converts an amount you have already chosen into units on a U-100 syringe. What it doesn't do: tell you what that amount should be. It's arithmetic, not medical advice.
1 What's in the vial
2 What each draw should contain
3 How much liquid to add
Each amount is shown in syringe units too, so you can measure the liquid with a syringe. Already mixed it? Just tap the amount you used.
All three syringe sizes are U-100: 100 units = 1 mL, so 1 unit = 0.01 mL. This is arithmetic on the markings, not advice about what to measure — for that, ask a licensed clinician and follow the labeling that came with your product.
What else this tool gets called
People look for this tool under a lot of names — reconstitution calculator, bac water calculator, peptide mixing calculator, mcg-to-units converter, peptide dosage calculator. They all describe the same two sums, and this page does both:
- Reconstitution — how much bac water to add to the powder, and what that makes each millilitre worth.
- Dose volume — turning an amount you have already decided on into a number of units to draw on a U-100 syringe.
The second one is a unit conversion: it takes your number and tells you where it lands on the barrel. It has no opinion about what your number should be, and it can't have one — that depends on things a web page doesn't know about you.
How much bac water for a 10 mg vial?
This is the most-asked version of the question, and the honest answer is that's your choice, and any of these are valid. Adding water doesn't change how much is in the vial — it only spreads the same amount across more liquid, so each marking on the syringe becomes worth less. You're choosing how easy the measurement is to read.
Here's what each choice actually does. Every cell is what one unit on a U-100 syringe is worth once mixed:
| Vial | + 1 mL | + 2 mL | + 3 mL | + 5 mL |
|---|---|---|---|---|
| 5 mg | 50 mcg | 25 mcg | 16.7 mcg | 10 mcg |
| 10 mg | 100 mcg | 50 mcg | 33.3 mcg | 20 mcg |
| 15 mg | 150 mcg | 75 mcg | 50 mcg | 30 mcg |
| 20 mg | 200 mcg | 100 mcg | 66.7 mcg | 40 mcg |
| 30 mg | 300 mcg | 150 mcg | 100 mcg | 60 mcg |
Read it as a trade-off, not a right answer. More water gives you finer control and easier-to-read numbers, but uses more of the vial's space and more bac water. Less water means fewer, bigger draws. The tidiest result is usually the one where your amount lands on a whole number of units — which is exactly what the calculator above marks for you.
Whatever your product's own instructions say overrides all of this, including the table.
Common questions
Is this a peptide dosage calculator?
It's the arithmetic half of one. Give it an amount and it converts that amount into units on your syringe, and works out how much bac water to add to get there. What it will never do is suggest what the amount should be — that's a decision for you and whoever prescribed or supplied your product, not for a calculator.
Does adding more bac water mean I'm taking more?
No — and this is the single most common misunderstanding. The vial contains what it contains. Water only changes the concentration, so a bigger volume means each unit on the syringe carries less. If you add twice the water, you draw twice the units for the same amount. The calculator does this conversion for you so the swap is obvious.
Can you add too much bac water?
Practically, yes — in two ways. The obvious one is physical: the vial only holds so much, and overfilling it pressurises the vial and pushes liquid back up the needle. Check the vial's capacity before choosing a volume; a 3 mL vial cannot take 5 mL.
The subtler one is readability. The more water you add, the smaller the number of units each draw becomes — and past a point your measurement lands on a sliver of a marking you can't read accurately. Diluting until a draw is one or two units defeats the purpose. If the calculator above shows your draw as a very small number, that's the signal to use less water, not more.
Too little has the mirror problem: the powder may not fully dissolve, and your draw becomes a large fraction of the vial. The readable middle is what the calculator is marking for you.
How many units is 250 mcg?
There's no fixed answer, because units measure volume, not amount. 250 mcg could be 5 units or 25 units depending entirely on how much water went into the vial. That's why the calculator asks for the vial size and the water volume before it can answer — put your numbers in above and it works out your particular case.
Does it work with 0.3 mL and 0.5 mL syringes?
Yes. All three standard insulin syringe sizes are U-100, meaning 100 units = 1 mL and one unit = 0.01 mL on every one of them. The barrel size only changes how many units fit and how far apart the markings are printed — a smaller barrel spreads the same units over more space, which is why tiny measurements are easier to read on a 0.3 mL. Pick your size in step 2 and the diagram redraws to match.
My answer lands between two markings. Now what?
That's the calculator telling you the volume you picked is awkward for the amount you want. Try a different amount of water — the row it highlights is the one that lands closest to a clean marking. Choosing a volume that gives you whole units is the whole point of doing this sum before you mix rather than after.
What is a U-100 syringe?
The standard insulin syringe scale: 100 units to 1 millilitre. It's called U-100 because it was designed for insulin at 100 units per mL, but the markings are just volume — one unit is 0.01 mL of whatever is in the barrel. The full conversion table has every marking written out.
Can I save or share my numbers?
Yes. The page remembers your last entry in your own browser, and Copy result gives you a line of text with the numbers worked out. The address bar also updates as you go, so bookmarking or sending the link brings the same figures back up for whoever opens it.
The supplies this assumes you have
Every answer above presumes mixing liquid and a unit-marked syringe on hand.