LabRatDailyPeptide reconstitution calculator
Enter what is in the vial, how much bacteriostatic water you added and your dose. It gives you the concentration, the millilitres to draw and the exact mark on the syringe. Free, no sign-up, and nothing you type leaves your browser.
Calculator
1 · The vial
Go by the barrel’s units-per-ml scale, not its size. A 0.5 ml or 0.3 ml insulin syringe is usually still U-100.
That makes 2.5 mg per ml.
2 · Each dose
Draw to 10 units
0.1 ml · 20 doses in a full vial
That draw is more than 1 ml, so it will not fit in one insulin syringe. Usually a sign the vial wants more water, or that a number is off.
For scale, at this concentration
| Draw | Units | Dose | Of vial |
|---|---|---|---|
| 1 ml | 100 | 2500 mcg | 50% |
| 0.75 ml | 75 | 1875 mcg | 37.5% |
| 0.5 ml | 50 | 1250 mcg | 25% |
| 0.25 ml | 25 | 625 mcg | 12.5% |
| 0.1 ml (your dose) | 10 | 250 mcg | 5% |
| 0.05 ml | 5 | 125 mcg | 2.5% |
Each row is one draw, with your dose highlighted. It shows what a step up or down on the barrel means in peptide terms.
Work backwards
For a draw that was not the usual dose.
How the maths works
Three steps, and the powder’s own volume is small enough to ignore:
- Concentration = peptide in the vial ÷ water added.
5 mg ÷ 2 ml = 2.5 mg/ml, which is 2500 mcg/ml. - Volume to draw = dose ÷ concentration.
250 mcg ÷ 2500 mcg/ml = 0.1 ml. - Syringe units = volume × the syringe scale. On a U-100 syringe, 100 units is 1 ml, so
0.1 ml × 100 = 10 units.
Doses per vial is the vial amount divided by the dose: 5 mg ÷ 0.25 mg = 20 doses.
Quick reference, U-100 syringe
Where common doses land for the two most common vial sizes. Concentration is in mg/ml. Each dose cell is the mark on the barrel, in units.
| Water | mg/ml | 250 mcg | 500 mcg | 1 mg |
|---|---|---|---|---|
| 1 ml | 5 | 5 | 10 | 20 |
| 2 ml | 2.5 | 10 | 20 | 40 |
| 2.5 ml | 2 | 12.5 | 25 | 50 |
| 3 ml | 1.67 | 15 | 30 | 60 |
| Water | mg/ml | 250 mcg | 500 mcg | 1 mg |
|---|---|---|---|---|
| 2 ml | 5 | 5 | 10 | 20 |
| 3 ml | 3.33 | 7.5 | 15 | 30 |
| 4 ml | 2.5 | 10 | 20 | 40 |
| 5 ml | 2 | 12.5 | 25 | 50 |
Mistakes that are easy to make
- mg and mcg. 1 mg is 1000 mcg. A 250 mcg dose is 0.25 mg. Mixing the two is the classic factor-of-a-thousand error, and it is why the calculator makes you pick a unit for the dose separately from the vial.
- U-100 against U-50. Only pick U-50 for a barrel marked 50 units per ml. A small 0.5 ml or 0.3 ml insulin syringe is almost always U-100, and treating it as U-50 doubles the draw.
- Reading “units” as peptide. Syringe units are marks on the barrel for volume. IU on a vial label is something else, and the two cannot be converted without the concentration.
- Tiny draws. If a dose comes out at 2 or 3 units it is hard to measure accurately. Unless you have been told a specific volume, adding more water so the dose lands on a bigger mark is the usual fix, as long as one draw stays under 1 ml.
- Trusting a number from a forum. “250 mcg is 10 units” is only true for one concentration. Check the vial and the water every time.
Questions
How many units is 250 mcg?
It depends on the concentration, which is the vial size divided by the water added. 5 mg in 2 ml gives 2.5 mg/ml, so 250 mcg is 0.1 ml, which is 10 units on a U-100 syringe. 5 mg in 1 ml makes it 5 units. 10 mg in 2 ml also makes it 5 units.
How much bacteriostatic water should I add to a 5 mg vial?
If your pharmacy or prescriber gave an amount, use that. Otherwise 1 to 3 ml is typical. 2 ml gives 2.5 mg/ml, which puts a 250 mcg dose at 10 units, an easy mark to read. More water means bigger, easier-to-measure draws for small doses. Less water means fewer draws per vial.
What is the difference between ml and units on a syringe?
Units on an insulin syringe are volume marks. On a U-100 syringe 100 units is 1 ml, so each unit is 0.01 ml. They are not a measure of peptide, and they are not the same as IU on a vial label.
Does this work for semaglutide, tirzepatide, BPC-157 or any other peptide?
Yes. The arithmetic only depends on the amount in the vial, the volume of water added and the syringe scale. It is the same for every lyophilised peptide.
How long does a reconstituted vial keep?
It varies by peptide and by who supplied it. Many pharmacies say 28 days in the fridge once mixed with bacteriostatic water, but follow the label or your pharmacy over any rule of thumb. The app tracks the discard date for you.
Is anything I type here saved or sent anywhere?
No. The calculator runs entirely in your browser. The numbers are put in the page address so you can bookmark or share a result, and nothing is stored on a server.
Keep the numbers with the log
LabRatDaily does this maths for every compound you take, shows how many doses are left in the open vial, warns you before it expires, and prints a summary for your doctor. It is free, has no account, and every record stays on your phone.
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