Educational reference only — not medical advice. This calculator does maths only and does not recommend any dose. Always confirm your dose and preparation with a licensed healthcare provider or pharmacist.
Reconstitution Calculator
Results update live as you type. Your dose must come from your prescription or provider — this tool never suggests one.
Printed on the vial label — the total powder in the vial.
The volume of bacteriostatic water you mix into the vial.
Enter the dose exactly as given to you. 1 mg = 1,000 mcg.
U-100 syringes: 100 units = 1 mL, whatever the barrel size.
Nothing you type leaves this page — the calculation runs entirely in your browser. Educational reference only, not medical advice.
Tirzepatide is a prescription medicine with a split personality: the approved version comes ready to inject, and the powder version sold online needs mixing. This page is for the powder only. If what you have is a Mounjaro or Zepbound pen, this calculator is not for you — and this page says so up front, because confusing the two is the easiest mistake to make here.
What is Tirzepatide?
Tirzepatide is a synthetic peptide that acts on two gut-hormone receptors at once — GIP and GLP-1. It was developed by Eli Lilly and is sold as Mounjaro and Zepbound. Mounjaro was approved in May 2022 for type 2 diabetes; Zepbound was approved in November 2023 for chronic weight management and in December 2024 for obstructive sleep apnoea in adults with obesity. Compounded tirzepatide is not FDA-approved, and the lyophilised powder vials sold online are not FDA-approved products and are not checked by a regulator for identity or purity.
Pens and branded vials — do not use this calculator.
Approved Mounjaro and Zepbound come as pre-filled single-dose pens and as single-dose vials (2.5, 5, 7.5, 10, 12.5 and 15 mg, each 0.5 mL). Those vials contain ready-made solution: nothing to reconstitute, and the whole vial is one dose. Zepbound also comes as a multi-dose vial and a single-patient-use KwikPen (four weekly doses each) — also ready-made. The numbers 2.5–15 mg are branded-product strengths, not powder-vial sizes. This calculator is only for lyophilised tirzepatide powder in vials.
The vial maths.
Powder vials are commonly sold as 5, 10, 15, 20, 30 and 60 mg. Because the vials are larger than most peptides’, the concentrations after mixing are higher and the mcg-per-unit figures are bigger — the formula, however, is unchanged.
Worked example — 20 mg vial, 2 mL of BAC water, example dose 2.5 mg:
- First convert the dose: 2.5 mg = 2,500 mcg
- Concentration: (20 × 1,000) ÷ 2 = 10,000 mcg/mL
- Each unit holds 10,000 ÷ 100 = 100 mcg
- Units for the example dose: 2,500 ÷ 100 = 25 units (0.25 mL)
- Doses in the vial: 20,000 ÷ 2,500 = 8 doses
A 30 mg vial in 3 mL gives the same 10,000 mcg/mL — the same concentration from a bigger vial. That is why the calculator asks for both numbers.
Storage (commonly cited):
Once mixed, refrigerate at 2–8 °C, protect from light, do not freeze. How long a mixed vial is said to keep varies a lot by source — most say around 28 days, one says 7–14 days, others cite 28–60 days or up to 90 days for compounded product. Do not treat any single figure as settled; your product’s own label takes precedence.
FAQs
My tirzepatide is a pre-filled pen. Does this page apply?
No. Approved pens are pre-mixed and deliver set doses — follow your prescription and the pen instructions. This calculator is only for powder vials mixed with bacteriostatic water.
What is the concentration of a 20 mg tirzepatide vial in 2 mL?
20 × 1,000 ÷ 2 = 10,000 mcg/mL. Each U-100 unit therefore contains 100 mcg, so your units = your dose in mcg ÷ 100. A dose of 2.5 mg (2,500 mcg) at this mix is 25 units.
My dose is written in mg. How do I enter it?
Either multiply by 1,000 to get mcg (2.5 mg = 2,500 mcg) or tap the mg toggle beside the dose field and type the mg figure directly — the calculator converts it for you.
Are the 2.5–15 mg strengths powder vials?
No. Those are the ready-made branded single-dose vials (0.5 mL each, whole vial = one dose). They need no mixing and no calculator.
Related calculators
See also the Semaglutide Calculator and the Peptide Calculator home page.
Educational reference only — not medical advice. This calculator does maths only and does not recommend any dose. Always confirm your dose and preparation with a licensed healthcare provider or pharmacist.