Dosage calculator
GLP-1 mg to units converter
Your prescription is written in milligrams. The syringe in your hand is marked in units. This converts between the two for compounded semaglutide and tirzepatide at any vial concentration, in either direction, so that the number your telehealth provider texted you is something you can check rather than something you have to trust.
The short answer to “how many units is 5 mg?”: it depends on the vial. At 10 mg/mL it is 50 units; at 5 mg/mL it is 100. The table below works out the usual doses. It is arithmetic, not dosing advice, and the dose itself comes from your prescriber.
Select your drug
Vial concentration (mg/mL)
Read this off the vial rather than assuming it. The concentration is printed on every compounded vial, and getting it wrong is where most dosing confusion begins.
What do you want to calculate?
The mark to draw to on your syringe
10units
= 0.100 mL drawn into a U-100 insulin syringe
Semaglutide dose → syringe units lookup
The FDA-approved titration steps, each turned into syringe units at the concentrations compounders most often use.
| Dose (mg) | @ 2.5 mg/mL | @ 5 mg/mL |
|---|---|---|
| 0.25 mg | 10 units | 5 units |
| 0.5 mg | 20 units | 10 units |
| 1 mg | 40 units | 20 units |
| 1.7 mg | 68 units | 34 units |
| 2.4 mg | 96 units | 48 units |
Units → semaglutide mg lookup
For the other direction: your prescriber names a number of units, and you want the milligrams behind it.
| Units drawn | @ 2.5 mg/mL | @ 5 mg/mL |
|---|---|---|
| 5 units | 0.13 mg | 0.25 mg |
| 10 units | 0.25 mg | 0.5 mg |
| 15 units | 0.38 mg | 0.75 mg |
| 20 units | 0.5 mg | 1 mg |
| 25 units | 0.63 mg | 1.25 mg |
| 30 units | 0.75 mg | 1.5 mg |
| 40 units | 1 mg | 2 mg |
| 50 units | 1.25 mg | 2.5 mg |
Why this tool exists
When the drug is a compounded semaglutide or tirzepatide, the instruction that arrives is almost never in milligrams. It is a mark on a syringe: draw to 40 units. Where the 40 came from generally goes unsaid, which is why so many people end up searching “how many mg is 40 units of semaglutide?” after the fact. That question has no single answer, because it turns entirely on one figure nobody thought to mention: the concentration of your vial, in milligrams per milliliter.
What follows is the arithmetic that should have come with the instruction. Choose the drug, set the concentration printed on your vial, and go whichever way you need: milligrams in for units out, or units in for milligrams out. Underneath, the usual doses and the usual unit counts are already worked out in lookup tables.
The math (so you can verify it yourself)
The syringe sent with a compounded GLP-1 vial is usually a U-100 insulin syringe, meaning its markings are set so that 100 units fill 1 mL and each unit is 0.01 mL. FDA’s alert on compounded semaglutide dosing errors describes exactly that: a U-100 (1 mL) syringe, on which a 5-unit dose is 0.05 mL [5]. Once that is fixed, the rest is division:
units = (dose in mg × 100) ÷ concentration in mg/mL
mg = (units × concentration in mg/mL) ÷ 100
Worked through: take compounded semaglutide at 2.5 mg/mL, on a starting dose of 0.25 mg a week, and you get
units = (0.25 × 100) ÷ 2.5 = 10 units
So the plunger stops at the 10-unit mark.
How many units is my dose?
The converter’s own results at the two concentrations most often sold for each drug. Anything over 100 units is more than 1 mL and will not fit in one U-100 syringe.
| Dose | At 2.5 mg/mL | At 5 mg/mL |
|---|---|---|
| 0.25 mg | 10 units | 5 units |
| 0.5 mg | 20 units | 10 units |
| 1 mg | 40 units | 20 units |
| 1.7 mg | 68 units | 34 units |
| 2.4 mg | 96 units | 48 units |
| Dose | At 5 mg/mL | At 10 mg/mL |
|---|---|---|
| 2.5 mg | 50 units | 25 units |
| 5 mg | 100 units | 50 units |
| 7.5 mg | 150 units (over 1 mL) | 75 units |
| 10 mg | 200 units (over 1 mL) | 100 units |
| 12.5 mg | 250 units (over 1 mL) | 125 units (over 1 mL) |
| 15 mg | 300 units (over 1 mL) | 150 units (over 1 mL) |
These figures are only right for the concentration in each column. Read your own vial’s label and enter it above.
Common compounded concentrations
There are only a handful of concentrations in general use. Across the compounded GLP-1 sellers on our register, two dominate for each molecule:
- Semaglutide: 2.5 mg/mL or 5 mg/mL, and 2.5 is what you will usually be sent. Certain 503A pharmacies move higher-dose patients onto 5 mg/mL so the volume drawn stays reasonable.
- Tirzepatide: 5 mg/mL or 10 mg/mL, and here the stronger one prevails. Even at 10 mg/mL, Zepbound's top dose of 15 mg a week comes to 150 units (1.5 mL), more than one 1 mL syringe holds; at 5 mg/mL it would be 300 units.
Switching concentration in the calculator is one click and everything recomputes as you do it. What it cannot do is read your vial. Check the label first, every time, and let that set the number rather than any figure on this page.
What can go wrong
More dosing mistakes come from one habit than any other: reusing a unit count (from a friend, or from the vial before this one) that was worked out at a different concentration. The same mark on the same syringe carries a different number of milligrams at each concentration, so a change nobody noticed can halve or double the dose while everything still looks exactly as it should. Four things to check:
- The concentration on the vial moved. A new label reading 5 mg/mL where the last said 2.5 mg/mL means the unit count you have been using now delivers twice the milligrams. Work it out again before you draw.
- The pharmacy behind it changed. One prescription filled by two compounders can arrive at two different default concentrations. Ask the new one what theirs is.
- The syringe is not a U-100. What ships with a compounded GLP-1 is, but a U-40 or a U-500 left over from veterinary or insulin supplies will not do the same arithmetic. Read what is printed on the barrel.
- The answer comes out above 100 units. That is more than 1 mL, and it will not fit in one insulin syringe. Two injections, a stronger vial from the pharmacy, or a 1 mL tuberculin syringe are the ways round it. Settle which with your prescriber rather than improvising.
Frequently asked questions
How many units is 5 mg?
It depends on the vial's concentration. At 10 mg/mL, 5 mg is 50 units on a U-100 syringe (0.5 mL). At 5 mg/mL it is 100 units, a full 1 mL syringe. At 2.5 mg/mL it would be 200 units, which does not fit in one syringe.
How many units is 2.5 mg of tirzepatide?
At 10 mg/mL, 2.5 mg is 25 units. At 5 mg/mL it is 50 units. Check the concentration printed on your vial before drawing.
How many units is 0.25 mg of semaglutide?
At 2.5 mg/mL, 0.25 mg is 10 units. At 5 mg/mL it is 5 units. FDA has reported patients who drew several times their intended dose after confusing units with milligrams or milliliters.
How do you convert mg to units?
Multiply the dose in mg by 100, then divide by the vial's concentration in mg/mL. The 100 comes from the U-100 syringe, which holds 1 mL across 100 units. To go the other way, multiply the units by the concentration and divide by 100.
How many mg is 40 units?
Multiply 40 by the concentration and divide by 100. At 2.5 mg/mL, 40 units is 1 mg; at 5 mg/mL it is 2 mg; at 10 mg/mL it is 4 mg. The same mark means a different dose at each concentration.
How much bacteriostatic water do I add to a GLP-1 vial?
That is reconstitution, a separate step. Use the GLP-1 reconstitution calculator for semaglutide or tirzepatide vials, or the peptide reconstitution calculator for other peptides, and follow the pharmacy's instructions.
Mixing a vial is covered by the GLP-1 reconstitution calculator and, for other peptides, the peptide reconstitution calculator.
Important safety disclaimer
This page does arithmetic. It does not check that the vial in front of you is the right vial, at the right concentration, in the right syringe, for the right person, at the right time. Those remain with your prescriber and with you. GLP Watchdog does not diagnose, does not treat, and does not tell you what to take. If anything about the dose is unclear, do not inject. Call your prescriber or the compounding pharmacy and get it confirmed first.
References
- 1.Novo Nordisk Inc. WEGOVY (semaglutide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215256s026lbl.pdf
- 2.Novo Nordisk Inc. OZEMPIC (semaglutide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/209637s035,209637s037lbl.pdf
- 3.Eli Lilly and Company. ZEPBOUND (tirzepatide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/217806s002lbl.pdf
- 4.Eli Lilly and Company. MOUNJARO (tirzepatide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215866s039lbl.pdf
- 5.U.S. Food and Drug Administration. FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products (describes a U-100, 1 mL insulin syringe and a 5-unit, 0.05 mL dose). FDA Human Drug Compounding. 2024. https://www.fda.gov/drugs/human-drug-compounding/fda-alerts-health-care-providers-compounders-and-patients-dosing-errors-associated-compounded
- 6.U.S. Food and Drug Administration. Compounded Drug Products — 503A and 503B Outsourcing Facility Information for Patients. FDA Drug Compounding Resources. 2024. https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers
Related tools and research
- GLP-1 dose plotter: each step of the ladder, plotted as it accumulates toward steady state.
- Compounded semaglutide bioequivalence: the testing a 503A or a 503B is actually obliged to do, and where the quality risk really sits.
- PCAB accreditation investigation: how to judge the pharmacy that fills your script.
- FDA warning letters database: check your seller against enforcement on the record.
- GLP-1 compounded pricing index: what the compounded telehealth market charges right now, end to end.
A weekly dose that has to be divided across several injections goes through the GLP-1 split-dose calculator.
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