Unit conversion
Pens do not need this. Vials do.
A single-dose pen delivers its stated dose and there is nothing to work out. Draw the same medication from a vial and you are suddenly converting milligrams into syringe units.
- Cost
- Free
- Syringe
- U-100
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- None
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The science
Why units and milligrams are different scales
01
Units on an insulin syringe measure volume, not mass. One hundred units is always one millilitre, whatever is dissolved in it. How much drug that contains depends entirely on the concentration.
02
That is why a dose written in milligrams cannot be read directly off a barrel. You need the concentration first: milligrams in the vial divided by millilitres of liquid.
03
Once you have concentration, dose divided by concentration gives the volume, and volume times one hundred gives the mark. A 30 mg vial in 2.4 ml is 12.5 mg/ml, so a 7.5 mg dose is 0.6 ml — 60 units.
04
If a dose lands below two units, reconstitute with more liquid. At that end of the scale the gap between graduations is a large share of the dose, and a small reading error becomes a large dosing one.
FAQ
Common questions
How many units is 2.5 mg of tirzepatide?
It depends on the concentration. A 30 mg vial reconstituted in 2.4 ml gives 12.5 mg/ml, so 2.5 mg is 0.2 ml — 20 units on a U-100 syringe. Change the liquid volume and the unit count changes with it.
Do I need to convert units if I use a Zepbound pen?
No. A pen delivers the stated dose with no measurement on your part. Conversion only applies when drawing from a vial.
What syringe should I use?
A U-100 insulin syringe is standard for these volumes because its graduations are fine enough to measure small amounts accurately. 0.5 ml and 0.3 ml syringes have finer markings again for very small doses.
Why does my dose land between two marks?
Because the concentration produces a volume that does not fall on a whole graduation. Changing the liquid volume shifts every dose onto different marks — the calculator shows which volumes land cleanly.
VialClock
This page calculates. Your notes app forgets.
Every tool here is stateless by design. What it cannot do is remember that your vial was mixed eleven days ago, or that a step-up is due this week.
Browse all calculatorsThis tool performs arithmetic on figures you enter, or presents a manufacturer-published schedule. It does not know your protocol, will never suggest a dose, and is not medical advice. Dosing decisions belong with a qualified prescriber.