Page last checked 2026-07-22

Reconstitution · Tirzepatide

Tirzepatide reconstitution calculator

Pick the vial, the water you added and the dose. Get the exact draw in units for the syringe in your hand.

Step 1 of 4

How many mg are in your vial?
Vial strengthamount printed on the vial
How many mL of water did you add?
Bacteriostatic water addedhow much water you added
What dose do you want to convert?
Target doseenter the dose you want to convert
mg
This vial holds 10 mg in total.
Which syringe are you using?
Syringe typematch the label on your syringe
U-100 insulin syringe · 1 mL · lines every 2 units · 1 unit = 0.01 mL

Draw to

50.0units

0.50 mL · 5.00 mg/mL · 50 mcg per unit · 4 doses per vial

Easy to read on this syringe. Draw to the 50-unit line. No rounding is needed.

10 mg ÷ 2 mL = 5.00 mg/mL
→ 50 mcg/unit · 2.5 mg = 0.500 mL = 50.0 units

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Show the math and syringe details

Can this syringe show the result clearly?

Easy to read on this syringe. 50.0 u is exactly the 50-unit line on a U-100 — no rounding error at all.

Want an easier syringe number?

This setup is already easy to read. Changing the water between 0.5 and 3 mL would not put 2.5 mg closer to a line on this U-100 syringe.

Adding more water makes the mixture less concentrated, so the same dose uses more syringe units. It does not change how much peptide is in the vial.

This setup is in the address bar — every input is part of the link.

Educational math, not medical advice — dosing decisions belong to a licensed clinician. The tabs above also plan a schedule week by week and count how many doses one vial holds.

How to use the calculator

STEP 1
Enter the amount in the vial
Use the total amount printed on the vial, in mg.
STEP 2
Enter the water you added
Use the amount of water added to that vial, in mL.
STEP 3
Enter the dose you want to convert
Choose mg or mcg, then match the result to your syringe.

Tirzepatide is the drug in Zepbound and Mounjaro. It works on two gut hormone signals involved in appetite and blood sugar. People take Zepbound for long-term weight management and Mounjaro for type 2 diabetes.

Both products have FDA approval and use weekly injections. Their labels cover different uses, so the product name matters.

Examples using a 10 mg Tirzepatide vial

Each row starts with the same 10 mg vial and changes only the amount of water. More water makes the mixture less concentrated, so the same dose uses more syringe units.

◆ How the water amount changes the resultdose used: 2.5 mg

For a 10 milligram vial: bacteriostatic water added, resulting concentration, micrograms per U-100 unit, and the draw for a 2.5 mg dose.
Water added	Concentration	Per U-100 unit	Draw for 2.5 mg	Nearest syringe line
1 mL	10.00 mg/mL	100.0 mcg	25.0 u · 0.250 mL	26 u · 4.0% off
2 mL	5.00 mg/mL	50.0 mcg	50.0 u · 0.500 mL	exactly 50 u
3 mL	3.33 mg/mL	33.3 mcg	75.0 u · 0.750 mL	76 u · 1.3% off

The vial, water and dose shown here are the calculator’s starting example for Tirzepatide. Replace them with your own values. Every result in the table is calculated from those inputs.

Drawn from once a week at 2.5 mg, a 10 mg vial yields 4 doses — about 4.0 weeks of supply. That lands exactly on the 28 days the mixed vial keeps for, so nothing is thrown away.

Five vial sizes, and the draw changes with all of them

Tirzepatide powder is sold in several vial sizes. The same dose can therefore take only a few syringe units or most of the syringe, depending on the vial strength and how much water was added.

3Open the mixing details — 3 notes

Why the sizes run so wide

FDA-approved tirzepatide arrives already mixed in a pen or single-dose vial. A vial of powder is a compounded presentation, not one of the approved products.

Compounded vials come in different strengths and sizes. That is why checking the label on the vial matters before entering any numbers.

The big vials squeeze the small doses

More powder in less water makes a stronger solution. A small dose may then use only a few syringe units, so a one-unit reading error matters more.

The calculator shows this clearly: changing the water changes the volume you draw, but not the amount of tirzepatide in the vial.

The mistake: carrying a unit count across a dose step

Tirzepatide’s schedule climbs over months. Same vial, same water, new dose — and a new unit count every time. A number that was right in week four is wrong by week eight, and it is wrong in the direction of drawing too little.

This is the compound where that trap is likeliest. It is the one people stay on longest while the dose keeps moving. Redo the arithmetic at each step rather than nudging the old figure.

The starting dose is only the first step

The calculator opens at the starting dose in the approved Zepbound schedule. That is the first step, not a long-term dose.

4Read the supporting evidence — 4 supporting notes

Starting, step-up and maintenance doses are different

The approved schedule begins with a low weekly starting dose. The label then raises it in equal steps after at least four weeks at the current dose.

The storage window is a general vial rule

The general storage window shown here comes from a pharmacy standard for opened multi-dose vials. It is not a tirzepatide stability study.

The calculator cannot check timing

Moving up a dose and handling a missed dose both depend on timing. The calculator does not know how long someone has used the current dose or when the last injection happened.

Powder vials are not an FDA-approved presentation

FDA-approved tirzepatide products arrive already mixed. A powder vial is compounded, so its strength and instructions come from the dispensing pharmacy rather than the Zepbound or Mounjaro package insert.

Units to dose at 5.00 mg/mL

Mix 10 mg into 2 mL and one U-100 unit carries 50.0 mcg. The table shows how much peptide is in each numbered syringe line. These are conversion examples, not suggested doses.

10Open the unit conversion table — 10 rows

Numbered U-100 syringe lines converted to volume and mass at 5.00 milligrams per milliliter.
U-100 line	Volume	Mass (mcg)	Mass (mg)
10 u	0.10 mL	500 mcg	0.5 mg
20 u	0.20 mL	1,000 mcg	1 mg
30 u	0.30 mL	1,500 mcg	1.5 mg
40 u	0.40 mL	2,000 mcg	2 mg
50 u	0.50 mL	2,500 mcg	2.5 mg
60 u	0.60 mL	3,000 mcg	3 mg
70 u	0.70 mL	3,500 mcg	3.5 mg
80 u	0.80 mL	4,000 mcg	4 mg
90 u	0.90 mL	4,500 mcg	4.5 mg
100 u	1.00 mL	5,000 mcg	5 mg

Where repeated Tirzepatide doses settle

Each weekly dose lands before the last one has cleared. So the level in the body climbs for a while, then holds steady. The half-life here is 5 days, which leaves 38% of a dose still there a week later. The level settles at about 1.61× what one dose gives. It gets 95% of the way there after 4 doses, roughly 3 weeks in.

9Open the weekly build-up table — 9 rows

For each dose: the estimated level just after it and just before the next dose, compared with the first dose, plus how close the peak is to the long-term level.
Dose	Level after	Level before the next	Share of long-term level
1	1.00×	0.38×	62%
2	1.38×	0.52×	86%
3	1.52×	0.58×	95%
4	1.58×	0.60×	98%
5	1.60×	0.61×	99%
6	1.61×	0.61×	100%
7	1.61×	0.61×	100%
8	1.61×	0.61×	100%
Plateau	1.61×	0.61×	100%

Half-life Tirzepatide prescribing information — DailyMed (NIH) · retrieved 2026-07-22. Every other figure is arithmetic on that half-life and the interval.

These are ratios, not blood levels. Turning them into an actual concentration would need more information than the cited source provides. The simple model is also only an approximation of how a drug really behaves in a body. The Accumulation tab plots the same math at whatever interval you pick.

How the math works

Concentration — divide the amount in the vial by the water you added: mg ÷ mL = mg/mL. This tells you how many mg are in each mL.
Volume — the dose divided by that concentration: dose ÷ (mg/mL) = mL.
Units — on a U-100 syringe one unit is 0.01 mL, so mL × 100 = units. A U-40 unit is 0.025 mL, so the wrong barrel is a 2.5× error. That is why the calculator asks which one you have.
Rounding gap — the exact draw against the nearest syringe line: |exact − nearest line| ÷ exact × 100 = % difference.

Medically reviewed by Jennifer Montecillo, MD · non-practicing medical reviewerReviewed 2026-07-22open the primary sources

Useful guides for this calculation

The math is only one part of the question. These guides cover the compound, published doses, side effects, mixing steps and supplies.

The tirzepatide titration schedule, step by step

All 6 steps from the tirzepatide label, with a source beside every row.

When tirzepatide reactions tend to appear

Information from an approved label behind the tirzepatide safety page.

How tirzepatide differs from the rest of its class

The FDA label gives a 6-step dosing schedule for tirzepatide.

Whether tirzepatide may still be compounded

The tirzepatide shortage was resolved on 2024-12-19, and every date after that turns on it.

Tirzepatide injection sites, timing and rotation

What the tirzepatide Instructions for Use specify, quoted rather than paraphrased.

The tirzepatide ladder in syringe units

All 6 rungs of the tirzepatide ladder, converted at one mix rather than described in general.

Questions readers ask

How do you calculate reconstitution?

Start with the concentration. Divide the vial strength by the water added to get mg/mL. Five vial sizes and three water amounts make fifteen possible concentrations.

Then units are dose divided by concentration, times 100. The 2.5 mg starting quantity is 4.2 units from a 60 mg vial in 1 mL. From a 5 mg vial in 3 mL it is 150 units, which does not fit a barrel.

How do I reconstitute 20 mg of tirzepatide?

For a 20 mg vial, 1 mL gives 20 mg/mL, 2 mL gives 10 mg/mL and 3 mL gives 6.67 mg/mL.

The 2.5 mg starting quantity then reads 12.5, 25 or 37.5 units. A 20 mg vial holds eight of those, and fewer as the schedule climbs. That climb is the trap here: same vial, same water, new dose, new unit count.

How much water to reconstitute 10 mg of tirzepatide?

With a 10 mg vial, adding 1, 2 or 3 mL produces concentrations of 10, 5 or 3.33 mg/mL. A 2.5 mg amount then draws 25, 50 or 75 units.

The whole span stays on one barrel, which is not true of the 5 mg vial at 3 mL. A 10 mg vial holds four starting doses. At the 15 mg maintenance quantity it does not hold one.

How to mix tirzepatide calculator?

Enter three things and the tool returns the fourth: vial strength, water volume and dose give the units. It also counts the doses in the vial and flags a draw too long for the barrel.

It cannot pick the dose. The labeled steps run 2.5 mg, then 5, 7.5, 10, 12.5 and 15 mg, no faster than four weeks apart. Those choices belong to a prescriber, and each step changes the unit count.

1primary source, each with the day we read it — open the documents used on this page

Zepbound (tirzepatide) — FDA-approved Prescribing Informationretrieved 2026-07-22FDA label