Reconstitution & syringe unit calculator
Turn a vial and a dose into the number of units to draw on a U-100 insulin syringe.
This is a converter, not dosing advice. It does arithmetic on numbers you already have. It cannot tell you what dose to take, whether a vial is safe, or how much water to add — those belong to you and your prescriber. Always confirm against your prescriber’s and your pharmacy’s instructions.
The calculator
Vial strength
Printed on the vial or the pharmacy label.
Total powder in the vial, before any water.
How much you reconstituted with.
Dose
mgAs prescribed to you.
Draw
Enter a strength and a dose.
How the maths works
There are only two steps, and neither is a secret — the value of a calculator like this one is that it does them without a slip, not that the arithmetic is hard.
Concentration. Reconstituting is plain division: the milligrams of powder in the vial divided by the milliliters of bacteriostatic water you add. 30 mg in 2 mL is 15 mg/mL. The water does not add to the amount of medication, only to the volume it is dissolved in, which is why the same vial can be any concentration you like.
Units. On a U-100 insulin syringe, 1 mL is 100 units, so the volume to draw is the dose divided by the concentration, and the unit count is that volume times 100. A 2.5 mg dose at 15 mg/mL is 0.17 mL, which is about 16.7 units.
U-100 is an assumption, and it is worth checking. The unit markings on an insulin syringe only mean milliliters if the syringe is a U-100 one, which is the common case and what this page assumes. A U-40 syringe carries the same numbers and they mean something else. If your syringe does not say U-100, the unit figure here does not apply to it — the milliliter figure still does.
Stop retyping it
Every calculator like this one, including this page, forgets your vial the moment you close the tab. If you are dosing weekly, that means entering the same two numbers every week and trusting that you entered them correctly at 6am, which is exactly the moment nobody wants to be doing mental arithmetic twice.
Logbook keeps the vial. It holds the containers you actually have — a vial, a pen, or a pack — counts each logged dose against whichever one you drew from, and tells you roughly how many doses are left and when you will run out.
On Android, this same calculator is built in, so the number you draw is one screen from the dose you log rather than in a browser tab. On iPhone it is not. The App Store allows a medication dosage calculator only from the company that makes the drug or an approved institution, and Logbook is neither — so on iPhone this page is the calculator, and everything else below is the same on both.
All of that is in the free version — the containers, the doses left, the run-out date, and the built-in calculator on Android. There is one optional unlock at $2.99 USD once, not $2.99 a month, for extras like the progress-photo timelapse and the insight charts. Everything stays on your phone, and there is no account.
If you are weighing it against the other GLP-1 trackers, I wrote an honest comparison of the field — including where the others are the better choice.
Android 8 or later · iPhone with iOS 15 or later