Before you draw
Zepbound comes in two kinds of vial, and they are drawn differently. A single-dose vial holds one dose in 0.5 mL. You draw all of it, which is the 50 mark on a U-100 syringe, whatever strength is printed on the vial. A multi-dose vial holds four doses in 2.4 mL, and the label describes each withdrawal as 0.6 mL, the 60 mark. So the correct mark for the same 2.5 mg prescription is 50 from one vial and 60 from the other. That difference is the reason this page exists.
Check the official label
Every number this page uses was read from these documents on 2026-09-04. The label is the authority; if it disagrees with this page, the label wins.
What the label says
Presentations from the current Zepbound label. Label strengths, quoted for comparison only: 2.5, 5, 7.5, 10, 12.5 and 15 mg once weekly. Your dose is whatever your prescriber wrote.
Where people go wrong with Zepbound vials
Drawing part of a single-dose vial. If your prescription is 2.5 mg and your vial is 2.5 mg, the draw is the whole vial. If your prescription is 2.5 mg and your vial says 5 mg, the label does not describe drawing half of it. The calculator will show 25 with a note saying so, and the note is not permission. Splitting a single-dose vial raises questions about sterility and how long the rest keeps that arithmetic cannot answer.
If the strength on your vial and the dose on your prescription differ, that is worth a call to the pharmacy before you draw anything: ask whether the whole vial is your dose. For a multi-dose vial the label answer is 0.6 mL, the 60 mark, four times. If the calculator shows anything else with a Zepbound vial selected, go back and check which vial you tapped.
If your vial is compounded
A compounded tirzepatide vial is not an FDA-approved product, and its concentration is whatever the pharmacy that made it chose, which changes the arithmetic. There is no strength to look up, so none of the presets above apply. Tap "My vial is not listed or is compounded", read the mg/mL off your own pharmacy label, and type it. If the label gives an amount and a volume instead, say 10 mg in 2 mL, divide first: 5 mg/mL. The calculator shows the millilitres beside the mark so you can compare with any instruction the pharmacy gave you in mL.
Worked answers
Three more questions
Which syringe does the Zepbound label describe?
A 1 mL syringe and needle. Most pharmacies hand over a U-100 insulin syringe, which holds 1 mL and is marked 0 to 100, and the 50 and 60 marks above assume that. If yours is marked to 50 or 30, it is the 0.5 mL or 0.3 mL size: the scale is the same, the 60 mark just does not exist on it.
How much bacteriostatic water do I add to tirzepatide?
None, for the approved product. Zepbound vials and Mounjaro pens are liquid and are never mixed. A tirzepatide powder is not an FDA-approved presentation; if a pharmacy dispensed one with mixing instructions, those instructions set the volume, and the powder option will do the division with their numbers.
Someone told me their dose in units. How do I compare?
You cannot, unless you know both concentrations. 20 units of a 5 mg/mL vial is 1 mg; 20 units of a 12.5 mg/mL vial is 2.5 mg. Compare in milligrams, and convert each through its own label.