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Zepbound calculator (tirzepatide)
Zepbound comes as a pen, but compounded/vialed tirzepatide needs reconstituting. Enter your vial mg, the bac water, and your dose for the exact units, mL, and doses per vial.
GLP-1/GIP (Mounjaro/Zepbound molecule; also compounded).
"Units" are a volume marking, not a drug amount — the same units = a different mg every time the vial is mixed differently.
Vial size × bacteriostatic water: what each combination gives you
The same vial gives a different concentration depending on how much water you add. Find your vial size and the water you added; the last column is what one milligram is worth in syringe units.
| Vial | Bac water added | Concentration | 1 mg draws |
|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 20 U |
| 5 mg | 2 mL | 2.5 mg/mL | 40 U |
| 5 mg | 3 mL | 1.67 mg/mL | 60 U |
| 10 mg | 1 mL | 10 mg/mL | 10 U |
| 10 mg | 2 mL | 5 mg/mL | 20 U |
| 10 mg | 3 mL | 3.33 mg/mL | 30 U |
| 15 mg | 1 mL | 15 mg/mL | 6.7 U |
| 15 mg | 2 mL | 7.5 mg/mL | 13.3 U |
| 15 mg | 3 mL | 5 mg/mL | 20 U |
| 30 mg | 1 mL | 30 mg/mL | 3.3 U |
| 30 mg | 2 mL | 15 mg/mL | 6.7 U |
| 30 mg | 3 mL | 10 mg/mL | 10 U |
| 60 mg | 1 mL | 60 mg/mL | 1.7 U |
| 60 mg | 2 mL | 30 mg/mL | 3.3 U |
| 60 mg | 3 mL | 20 mg/mL | 5 U |
Units are for a standard U-100 insulin syringe, where 100 units = 1 mL. These are conversions, not dose suggestions — your dose comes from your prescriber, and this page never proposes one. For a size or volume not listed, use the calculator above.
Zepbound vs Mounjaro: same molecule, different product
Zepbound and Mounjaro are both tirzepatide, so the reconstitution arithmetic above is identical for either. The products are not identical. These are the handling rules each one's own FDA label sets — the differences that a shared molecule name hides.
| Product | Presentation | Before use | Once in use |
|---|---|---|---|
| Zepbound | single-dose pen or vial | 2–8 °C | 21 days · ≤30 °C |
| Zepbound | opened multi-dose vial or KwikPen | 2–8 °C | 30 days · ≤30 °C Or 30 days after first use, or after 4 weekly doses — whichever comes first. |
| Mounjaro | single-dose pen or vial | 2–8 °C | 21 days · ≤30 °C |
| Mounjaro | opened multi-dose vial or KwikPen | 2–8 °C | 30 days · ≤30 °C Or 30 days after first use, or after 4 weekly doses — whichever comes first. |
In this case the labels agree: Zepbound and Mounjaro set the same in-use windows, word for word. Whatever separates these two products, it is not how you store them. More on the storage page.
Dosing is once weekly, and the published half-life of tirzepatide is ~120 h.
Where each one is actually sold
Same molecule does not mean same product on the shelf. These are the markets each brand is marketed in, per the national regulator's own register.
| Product | US | UK | Germany | Japan | Australia |
|---|---|---|---|---|---|
| Zepbound | Yes | No | No | Yes | No |
| Mounjaro | Yes | Yes | Yes | Yes | Yes |
Zepbound is marketed in US, Japan, but not in UK, Germany, Australia. In those countries the same molecule is sold as Mounjaro — so a Zepbound question asked from there is usually really a Mounjaro question.
Researched 2026-07-12 across five markets. A brand is only marked absent on positive evidence — no register entry, or a formal discontinuation. Availability changes; check your own country's register before relying on this.
Register sources: MHRA (GOV.UK) · EMA EPAR — Mounjaro · TGA AusPAR — Mounjaro
Label sources: Mounjaro FDA label (DailyMed), §16.2 · Zepbound FDA label (DailyMed), §16.2
FAQ
How many units is my dose?
Units are a volume marking on the syringe, not a drug amount — on a U-100 syringe, 100 units = 1 mL. The units for any dose depend entirely on how the vial was reconstituted (mg of powder ÷ mL of bacteriostatic water). Enter your numbers above and the calculator gives the exact units.
How much bacteriostatic water should I add?
There's no single right amount — more water makes the solution more dilute (easier to draw, larger volume per dose) and less water makes it more concentrated. Pick a volume, enter it above, and the calculator shows the resulting concentration, units per dose, and doses per vial so you can choose a readable draw.
How long can Zepbound stay out of the fridge?
Per its own FDA label, once in use — single-dose pen or vial: 21 days, ≤30 °C; opened multi-dose vial or KwikPen: 30 days, ≤30 °C. Unopened it stays at 2–8 °C. Always follow the carton you actually have; this is a restatement of the label, not advice.
Is Zepbound the same as Mounjaro?
Both are tirzepatide, and on storage their labels agree: the same presentations with the same in-use windows. The reconstitution arithmetic is identical too.
Where is Zepbound available?
Of the five markets we track, Zepbound is marketed in US, Japan and not in UK, Germany, Australia, per each country's own regulator register. Where it is absent, the same molecule is sold as Mounjaro.
Other calculators
Keep reading
Sources
This tool converts the numbers you enter — it never recommends a dose. Its constants are cited below; the warnings are arithmetic checks, not clinical limits.
- Syringe "units" are a volume marking, not a drug amount: a U-100 syringe reads 100 units = 1 mL (U-40 = 40 units/mL). The calculator converts mg ↔ mL ↔ units on this standard — it never assumes units equal mg.Standard insulin concentration, U-100 = 100 units/mL (PMC5505430) ↗
- The volume to draw is (drug ordered ÷ drug available) × the vial's total mL — i.e. dose ÷ concentration, where concentration (mg/mL) = vial mg ÷ bacteriostatic water mL. You enter every number; the tool only does this arithmetic.Dose-volume formula — StatPearls "Dose Calculation" (Bookshelf NBK430836) ↗
- An opened (punctured) multi-dose vial is dated and discarded within 28 days unless the manufacturer states otherwise.CDC Injection Safety (per USP General Chapter <797>) ↗
Educational calculator only — not medical advice and not a recommended dose. You enter your own numbers; we only do the arithmetic. Some products are not approved for human use; verify your product and dose with a licensed clinician.
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