Peptide reconstitution calculator
The method is two divisions. Mixing: the amount in the vial ÷ the water added = the strength, so a 10 mg vial mixed with 2 mL of water is 5 mg per mL. Reading: on a U-100 insulin syringe 1 unit is 0.01 mL, so each unit holds one hundredth of that strength, 50 mcg in this example.
Say what's in the vial and what each draw should contain. It shows the draw each common amount of liquid gives on your syringe, says which ones land on a printed line, and marks the easiest to measure. When none of them lands on a line, it looks for an amount between 0.5 and 10 mL that does.
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
IU are the product's own measure; the units here are the marks on the syringe.
3 How much liquid to add
Each amount shows the draw it gives on your syringe. Already mixed it? Tap the amount you used, or type it below.
All four syringe options are U-100: 100 units = 1 mL, so 1 unit = 0.01 mL. The difference between them is how finely the barrel is printed: a line every 2 units on the 1 mL, every unit on the 0.5 and 0.3 mL, and every half unit on the half-unit 0.3 mL barrel, so "easiest to measure" lands on different amounts of liquid. A draw counts as readable when it lands exactly on a printed line at least two lines up the barrel, and amounts a 3 mL vial can hold come first. 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. 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.
Peptide reconstitution chart
What one unit on a U-100 insulin syringe is worth once a vial is mixed, for common vial sizes and amounts of water. It is the concentration after mixing, not an amount to draw.
| Vial | + 1 mL | + 2 mL | + 3 mL | + 5 mL |
|---|---|---|---|---|
| 2 mg | 20 mcg | 10 mcg | 6.7 mcg | 4 mcg |
| 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 |
Each cell is micrograms per unit. Multiply by 100 for micrograms per mL, or divide the vial's milligrams by the millilitres of water for mg per mL: a 10 mg vial with 2 mL of water is 5 mg per mL.
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 volume your vial can hold is valid (a 3 mL vial takes about 3 mL at most). 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.
Read the chart as a trade-off, not a right answer. More water makes each draw a bigger number of units, which is easier to read, but it takes up more of the vial and uses more bac water. Less water makes each draw a smaller number of units of stronger liquid. The number of draws in the vial is the same either way. The tidiest result is the one where your amount lands on a printed line of your syringe: every 2 units on a 1 mL barrel, every unit on a 0.3 or 0.5 mL, every half unit on a half-unit 0.3 mL. The calculator above marks the amount of water that lands on a line, and when none of the usual amounts does, it looks for one that does.
Whatever your product's own instructions say overrides all of this, including the chart.
Common questions
Will this tell me how much to take?
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 second is the size of each draw. The more water you add, the more units each draw takes (twice the water, twice the units), so past a point a single draw no longer fits the syringe barrel. If the calculator above says the draw is over the syringe, that's the signal to use less water.
Too little has the mirror problem: the powder may not fully dissolve, and each draw shrinks to a line or two on the barrel, which is hard to read accurately. If the calculator above says the draw is too small, that's the signal to use more water, not less. The readable middle is what the calculator marks for you: an amount of water that puts the draw on a printed line of your syringe, preferring amounts a 3 mL vial can hold.
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 what's in the vial and then shows the draw for each amount of water — put your numbers in above and it works out your particular case.
Does it work with IU?
Yes. Pick IU for the vial and for the draw. The arithmetic is the same: IU in the vial ÷ mL of water added = IU per mL, and each syringe unit (0.01 mL) holds a hundredth of that. IU cannot be turned into mg without the product's own figure, so the two boxes are always in the same unit.
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 one it marks lands on a printed line of your syringe, and if none of the usual amounts does, it suggests one that does whenever there is one. Choosing a volume that lands on a line 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. Copy result gives you a line of text with the numbers worked out, and Copy link gives a link that opens the same numbers on the same syringe for whoever you send it to. The address bar also updates as you go, so a bookmark brings the same figures back up.
The supplies this assumes you have
Every answer above presumes mixing liquid and a unit-marked syringe on hand.