Math onlyTirzepatide is a prescription medicine, approved by the FDA as Zepbound (weight reduction and sleep apnea) and Mounjaro (type 2 diabetes).[1][2] This calculator converts a dose you already have into a volume. It does not choose or change a dose.
How to use the tirzepatide calculator
Using the calculator takes four inputs: the mg in the vial, its volume, your dose and your syringe size.
- Tirzepatide in the vial: the total mg in the vial. If the label gives a strength per mL, such as "10 mg/mL", enter 10 mg here and 1 mL below.
- Liquid in the vial: the mL that the mg is dissolved in.
- Dose: the mg your prescriber gave you.
- Syringe: the size of your U-100 insulin syringe, so the picture matches what you hold.
The default numbers are a 10 mg multi-dose vial, which holds four 2.5 mg doses in 2.4 mL.[1] That is 10 ÷ 2.4 = 4.17 mg/mL, so 2.5 mg is 0.6 mL, or 60 units on a U-100 syringe. The label itself measures that dose as 0.6 mL on a 1 mL syringe; it never mentions units.[1]
Approved vials: one fixed volume per dose
Every FDA-approved tirzepatide product is a ready-to-use solution with a fixed volume per dose, so no approved form needs a calculation:[1][2]
| Presentation | Doses | Volume per dose | On a U-100 scale |
|---|---|---|---|
| Single-dose pen | 1 | 0.5 mL | Not measured (autoinjector) |
| Single-dose vial | 1 | 0.5 mL (inject it all) | 50 units |
| Multi-dose vial (approved Jan 2026) | 4 | 0.6 mL | 60 units |
| KwikPen | 4 fixed doses | 0.6 mL | Not measured (dial pen) |
Each of these comes in one strength per vial or pen, from 2.5 mg to 15 mg. A 5 mg single-dose vial holds 5 mg in 0.5 mL; a 5 mg multi-dose vial holds four 5 mg doses in 2.4 mL.[1][3] Units on a U-100 syringe are a volume (100 units = 1 mL).[4]
Unit math matters when a solution's strength does not line up with a fixed dose, such as a compounded vial. Compounded tirzepatide is not FDA-approved, and since the national shortage ended the FDA has limited when it may be made.[7][6] See compounded tirzepatide: FDA status.
The label dose schedule
Both labels start at 2.5 mg once weekly, then increase in 2.5 mg steps after at least 4 weeks on each dose, up to 15 mg.[1][2]
- 2.5 mgWeeks 1–4 · starting dose
- 5 mgFrom week 5 at the earliest
- 7.5 mgFrom week 9 at the earliest
- 10 mgFrom week 13 at the earliest
- 12.5 mgFrom week 17 at the earliest
- 15 mgFrom week 21 at the earliest · maximum
The full chart, with the maintenance doses each label lists, is on the dosage chart page.
Label doses in units at common concentrations
At 10 mg/mL each label dose in units is ten times the mg: 2.5 mg is 25 units and 7.5 mg is 75 units.
| Dose | 5 mg/mL | 10 mg/mL | 20 mg/mL | 30 mg/mL |
|---|---|---|---|---|
| 2.5 mg | 50 | 25 | 12.5 | 8.3 |
| 5 mg | 100 | 50 | 25 | 16.7 |
| 7.5 mg | >100 | 75 | 37.5 | 25 |
| 10 mg | >100 | 100 | 50 | 33.3 |
| 12.5 mg | >100 | >100 | 62.5 | 41.7 |
| 15 mg | >100 | >100 | 75 | 50 |
More concentrations, and the reverse direction, are in the units to mg chart.
What the main weight trial found
In SURMOUNT-1, 2,539 adults with obesity or overweight took tirzepatide or placebo for 72 weeks. Average weight change was −15% on 5 mg, −19.5% on 10 mg and −20.9% on 15 mg, against −3.1% on placebo (treatment-regimen estimand).[5] The most common side effects were stomach-related: nausea, diarrhea, vomiting and constipation.[1] See trial results and side effects by dose.
Every guide on this site
The site has 33 guides in three groups: dose math, products and prices, and evidence.
Dose math
- Tirzepatide peptideWhat it is, how it works, brand names
- What is Zepbound?Uses, doses, results and key dates
- Units for each dose2.5 mg to 15 mg in every vial type
- Units to mg chartBoth directions, every concentration
- Dosage chartThe label escalation, week by week
- Bac water calculatorMixing math for powder vials, with FDA status
- Missed doseThe 4-day rule on a calendar
- Half-lifeHow much is left, day by day
- Mounjaro dosage chartType 2 diabetes doses, adults and children
Products and prices
- Zepbound vial guideSingle-dose and multi-dose vials
- Zepbound KwikPenFour fixed doses, priming and storage
- Pen vs vialAll four presentations compared
- Injection sitesAbdomen, thigh, arm and rotation
- Zepbound costSelf-pay and list prices, per dose and per mg
- Insurance coverageMedicare, the $50 Bridge, Medicaid
- Generic ZepboundPatents, exclusivity and filings
- Compounded tirzepatideFDA status and warning letters
- Compounded tirzepatide dosageStarting dose and unit math
- Compounded vs ZepboundEight documented differences
- Tirzepatide pillsWhy there is no oral tirzepatide
- Microdosing tirzepatideWhat the evidence shows
Evidence and comparisons
- Zepbound side effectsThe label tables for 5, 10 and 15 mg
- Tirzepatide side effectsMounjaro and Zepbound data, fatigue, safety
- Mounjaro side effectsThe diabetes label, symptom by symptom
- How long side effects lastWeek-by-week timeline
- Side effects in femalesHair loss, birth control, pregnancy
- Zepbound and alcoholWhat the label and NIH say
- Weight loss resultsSURMOUNT-1 by dose, and after stopping
- Sleep apneaThe 10 or 15 mg OSA dose and results
- Zepbound vs MounjaroSame molecule, different labels
- Zepbound vs WegovyHead-to-head results, doses and prices
- Foundayo vs ZepboundDaily pill vs weekly shot
- Tirzepatide vs semaglutideThe head-to-head trials
Frequently asked questions
How many units is 2.5 mg of tirzepatide?
From a 2.5 mg single-dose vial it is the whole vial: 0.5 mL, or 50 units on a U-100 scale. From a 10 mg multi-dose vial it is 0.6 mL, or 60 units. From a 10 mg/mL solution it is 25 units. See 2.5 mg in units.
How do I calculate tirzepatide units?
Divide the dose in mg by the concentration in mg/mL to get mL, then multiply by 100 for a U-100 syringe. 5 mg at 10 mg/mL: 5 ÷ 10 = 0.5 mL = 50 units.
Is tirzepatide FDA-approved?
Does this calculator recommend a dose?
No. It converts the dose you enter into a volume. Your dose comes from your prescriber and the product label.
Sources
- Zepbound (tirzepatide) injection: prescribing information, Medication Guide and Instructions for Use
- Mounjaro (tirzepatide) injection: prescribing information and Instructions for Use
- Zepbound supplement approval letter S-037 (multi-dose vial)
- FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1)
- FDA's concerns with unapproved GLP-1 drugs used for weight loss
- Declaratory order: resolution of shortages of tirzepatide injection products (Mounjaro and Zepbound)