How many units is 2.5 mg of Tirzepatide?

It depends entirely on how much water you added. In a 30 mg vial reconstituted with 3 mL, the concentration is 10 mg/mL, so 2.5 mg is 0.25 mL, which is 25 units on a U-100 insulin syringe. In the same vial with 1.5 mL of water it is 12.5 units, and with 4.5 mL it is 37.5 units.

How much bacteriostatic water for a 30 mg Tirzepatide vial?

3 mL is the usual choice. It gives 10 mg/mL, which puts the commonly reported range of 1 mg to 15 mg between roughly 10 and 150 units. Aim for a draw between about 10 and 50 units, where the barrel is easiest to read, and add or remove water to get there.

How many doses are in a 30 mg vial?

Divide 30 by your dose. At 2.5 mg that is 12 doses, which at once weekly is 84 days.

Is compounded tirzepatide the same as the licensed product?

No. Concentration, excipients and quality control differ. Anything you reconstitute yourself is at a concentration you chose, so unit counts from a pen do not transfer.

Tirzepatide dosage calculator

In a 30 mg vial with 3 mL of water (10 mg/mL), 2.5 mg of Tirzepatide is 25 units on a U-100 insulin syringe. The whole 2.5 to 15 mg ladder, converted into the mark on your syringe. Works for 10, 20, 30 and 60 mg vials.

Reviewed 3 September 2026
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Dose to units at the usual vial and water

Dose	U-100 units	Draw	Doses per vial	Vial lasts
2.5 mg	25 units	0.25 mL	12	84 days
5 mg	50 units	0.5 mL	6	42 days
7.5 mg	75 units	0.75 mL	4	28 days
10 mg	100 units	1 mL	3	21 days
12.5 mg	125 units	1.25 mL	2	14 days
15 mg	150 units	1.5 mL	2	14 days

30 mg vial in 3 mL of bacteriostatic water (10 mg/mL), U-100 insulin syringe, once weekly.

About Tirzepatide

Tirzepatide is a dual GIP and GLP-1 receptor agonist. The licensed titration ladder steps every four weeks: 2.5, 5, 7.5, 10, 12.5 and 15 mg once weekly, with 2.5 mg treated as a starting dose rather than a maintenance one.

Note that the licensed product is a pre-filled pen at a fixed concentration. Reconstituting a vial yourself means you set the concentration, so the unit numbers below will not match anything printed on a pen.

Switching from a pen or a Lilly vial to a vial you mixed

Every US Mounjaro and Zepbound single-dose pen, and every Zepbound single-dose vial, holds one dose in the same 0.5 mL. Lilly changes the strength, not the volume: 2.5 mg/0.5 mL is 5 mg/mL, and 15 mg/0.5 mL is 30 mg/mL. So on the licensed product you always injected 0.5 mL, which is 50 units on a U-100 insulin syringe, whatever your dose was. A vial you reconstitute yourself is the other way round: one concentration for every dose, so the volume changes with the dose. Your old 0.5 mL tells you nothing about the new draw.

Weekly dose	Licensed pen or vial	30 mg vial + 3 mL (10 mg/mL)	60 mg vial + 3 mL (20 mg/mL)	10 mg vial + 2 mL (5 mg/mL)
2.5 mg	5 mg/mL, 0.5 mL (50 units)	25 units	12.5 units	50 units
5 mg	10 mg/mL, 0.5 mL (50 units)	50 units	25 units	100 units
7.5 mg	15 mg/mL, 0.5 mL (50 units)	75 units	37.5 units	150 units (over one 1 mL syringe)
10 mg	20 mg/mL, 0.5 mL (50 units)	100 units	50 units	200 units (over one 1 mL syringe)
12.5 mg	25 mg/mL, 0.5 mL (50 units)	125 units (over one 1 mL syringe)	62.5 units	more than the vial holds
15 mg	30 mg/mL, 0.5 mL (50 units)	150 units (over one 1 mL syringe)	75 units	more than the vial holds

Units on a U-100 insulin syringe (100 units = 1 mL). The licensed column is from Lilly's Zepbound vial instructions; pens use the same 0.5 mL per dose.

Three worked examples

5 mg, from a 30 mg vial with 3 mL. 30 ÷ 3 is 10 mg/mL, the same strength as the licensed 5 mg dose (5 mg in 0.5 mL). 5 mg ÷ 10 mg/mL is 0.5 mL, so the mark is 50 units, the one case where the familiar 50 is right.

7.5 mg, same 30 mg vial. Still 10 mg/mL, so 7.5 mg is 0.75 mL: 75 units, not 50. From a 60 mg vial with 3 mL (20 mg/mL) it is 37.5 units.

15 mg. At 10 mg/mL that is 1.5 mL, 150 units, more than a 1 mL syringe holds. A 60 mg vial with 3 mL puts it at 75 units, and 12.5 mg at 62.5 units, so the top of the ladder fits one draw.

Mistakes that come from the pen

Drawing 50 units for every dose. 50 units was only ever 0.5 mL. On a vial you mixed, 50 units is your dose only when the vial's mg per mL is twice your dose in mg.
Using your own maths on a pharmacy vial. A compounded vial that arrives already in solution has its strength printed on the label (for example 10 mg/mL). Use that number; there is no water to add.
A 0.3 mL syringe for a big dose. A 0.3 mL (30 unit) syringe cannot hold 37.5 or 75 units in one draw. Match the syringe to the mark before you start.
Reading units as milligrams. "25 units" is 0.25 mL. At 10 mg/mL it is 2.5 mg; at 20 mg/mL it is 5 mg. Without the concentration the number means nothing. The FDA has received reports of dosing errors, some needing hospital care, from people measuring their own doses of compounded GLP-1 drugs.

Sources

Lilly: Zepbound single-dose vial, Instructions for Use. Six strengths, 2.5 to 15 mg, each in 0.5 mL; a 1 mL syringe.
FDA: concerns with unapproved GLP-1 drugs used for weight loss. Dosing-error reports with compounded products, some needing hospital care; discard a multi-dose vial 28 days after first use.

The same 30 mg vial at other water volumes

If the draw is awkward to read, change the water, not the dose. The dose stays the same; only the mark moves.

Vial	BAC water	Concentration	Draw	U-100 units	Doses/vial
30 mg	2 mL	15 mg/mL	0.167 mL	16.7 units	12
30 mg	3 mL	10 mg/mL	0.25 mL	25 units	12
30 mg	5 mL	6 mg/mL	0.417 mL	41.7 units	12
60 mg	2 mL	30 mg/mL	0.083 mL	8.3 units	24
60 mg	3 mL	20 mg/mL	0.125 mL	12.5 units	24
60 mg	5 mL	12 mg/mL	0.208 mL	20.8 units	24

All rows above assume a 2.5 mg dose and a standard U-100 insulin syringe, where 100 units = 1 mL.

How long it lasts in the body

The half-life of Tirzepatide is about 5 days. That is the time for the amount in your blood to halve, so after one half-life you are at 50 percent of the peak, after two you are at 25 percent, and after four you are at roughly 6 percent. This is why a weekly compound still has meaningful levels present when the next dose lands, and why levels build over the first several weeks before they settle.

Common questions

How many units is 2.5 mg of Tirzepatide?: It depends entirely on how much water you added. In a 30 mg vial reconstituted with 3 mL, the concentration is 10 mg/mL, so 2.5 mg is 0.25 mL, which is 25 units on a U-100 insulin syringe. In the same vial with 1.5 mL of water it is 12.5 units, and with 4.5 mL it is 37.5 units.
How much bacteriostatic water for a 30 mg Tirzepatide vial?: 3 mL is the usual choice. It gives 10 mg/mL, which puts the commonly reported range of 1 mg to 15 mg between roughly 10 and 150 units. Aim for a draw between about 10 and 50 units, where the barrel is easiest to read, and add or remove water to get there.
How many doses are in a 30 mg vial?: Divide 30 by your dose. At 2.5 mg that is 12 doses, which at once weekly is 84 days.
Is compounded tirzepatide the same as the licensed product?: No. Concentration, excipients and quality control differ. Anything you reconstitute yourself is at a concentration you chose, so unit counts from a pen do not transfer.

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The maths is openThe formula is on every page and in the methodology. The code is one file with an automated test suite, run before each deploy.

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ReviewedDose ranges and half-lives checked 3 September 2026.

Buying Tirzepatide?

Peptulator does not list, rank or link vendors. Whoever the supplier is, use the strength printed on your own vial and check the batch certificate of analysis before you rely on any number here.

The Tirzepatide guideDosing, evidence and side effects, at Peptide Bureau Read a syringeU-100 vs U-40, and the 2.5x error Build a full protocolThe stack builder at Peptide Bureau, about two minutes

Common conversions

The same three-step maths, pre-filled for the doses people ask about most. Units on a U-100 insulin syringe, where 100 units is 1 mL.

mg to units calculator Any dose at any concentration, both directions, with the full reference tables
Units to mg calculator What the units you drew are in milligrams
1 mg to units The most-asked conversion, at every common setup

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Before you use these numbers This is a unit-conversion tool. It turns a vial strength and a water volume into a concentration, a draw volume and a syringe mark. It does not tell you what to take, whether to take it, or whether a compound is safe for you. Most compounds listed are sold for laboratory research and are not approved for human use. Nothing here is medical advice. Dosing decisions belong with a licensed clinician who knows your history. Always check the strength printed on your own vial rather than trusting a preset.