Semaglutide Dose Calculator: Convert mg to Units for Compounded Vials

How many units of semaglutide is 0.25 mg?

It depends on the concentration of the vial, so no single unit count is correct. On a U-100 syringe, 100 units equal 1 mL,^[7] and units equal the dose divided by the concentration, times 100. At 1 mg/mL a 0.25 mg dose is 0.25 mL, or 25 units. At 2.5 mg/mL, which is a 5 mg vial mixed with 2 mL, it is 0.1 mL, or 10 units. At 5 mg/mL, which is a 10 mg vial mixed with 2 mL, it is 0.05 mL, or 5 units. The same dose therefore spans a five-fold range of syringe marks. The FDA has warned that product concentrations vary by compounder and that one compounder may offer several.^[3] Enter the vial milligrams, the water volume, and the dose your prescriber gave you. Then compare the concentration the calculator shows with the label on your vial before you draw anything.

Do you need a dose calculator for Ozempic or Wegovy?

No. Ozempic and Wegovy are FDA-approved semaglutide injections delivered by preset-dose injection pens designed for weekly dosing.^[3] Ozempic is supplied in single-patient-use pens that hold several weekly doses, in strengths of 2 mg per 3 mL, 4 mg per 3 mL, or 8 mg per 3 mL.^[1] Wegovy is supplied as single-dose pens and as a single-patient-use pen with four doses.^[2] You dial or press the pen as its instructions say. You never convert milligrams to syringe units, and you never draw from a vial. This calculator is for people who have been prescribed semaglutide in a vial that must be drawn with a syringe, where the unit count depends on the concentration the pharmacy chose. If you use a pen, follow the pen's instructions for use and ask your pharmacist about anything unclear.

Why do compounded semaglutide doses cause errors?

Three things combine: several concentrations, three kinds of measure, and a syringe scale that is easy to misread. In its 2024 alert, the FDA said that patients measured wrong doses and that providers miscalculated doses. It described patients given a U-100 syringe and told to draw 5 units, which is 0.05 mL, who instead drew 50 units, and it reported patients taking five to 20 times the intended dose.^[3] Here are the numbers. At 5 mg/mL, a 0.25 mg dose is 5 units. Drawing 50 units gives 2.5 mg, which is ten times that dose. The FDA also reported adverse events, some needing hospitalization, linked to dosing mistakes with compounded semaglutide.^[4] The alert tells patients to talk with their health care provider or compounder about how to measure and give the intended dose.^[3] A calculator removes arithmetic slips only. It cannot catch a wrong concentration on a label.

What does the FDA say about compounded semaglutide in 2026?

As of October 2026, the FDA states that compounded drugs are not FDA approved, which means the agency does not review them for safety, effectiveness, or quality before they are marketed.^[4] It declared the semaglutide injection shortage resolved on February 21, 2025, and said that compounders can no longer regularly make semaglutide unless they meet specific exemptions, such as a prescriber documenting a significant difference for an individual patient.^[5] On April 30, 2026, the FDA proposed to exclude semaglutide, tirzepatide, and liraglutide from the 503B bulks list. The comment period ended June 29, 2026, and the agency said it would consider comments before a final decision, so this is a proposal and not a final rule.^[6] The FDA also notes that semaglutide sodium and semaglutide acetate are different active ingredients, and that it has no information on whether they share the approved drug's properties.^[4] Check these pages for updates.

What is the FDA-label dose schedule for semaglutide?

The two approved brands use different schedules, and both are set by the prescriber. The Ozempic label says to start at 0.25 mg injected under the skin once weekly for 4 weeks, then raise to 0.5 mg, with later steps of 1 mg and then 2 mg; the maximum recommended dose is 2 mg once weekly.^[1] The Wegovy label steps through 0.25 mg in weeks 1 to 4, 0.5 mg in weeks 5 to 8, 1 mg in weeks 9 to 12, and 1.7 mg in weeks 13 to 16, with maintenance at either 1.7 mg or 2.4 mg, and 2.4 mg is the recommended one. The label also allows an increase to a maximum of 7.2 mg once weekly for those who tolerate 2.4 mg for at least 4 weeks and need more weight reduction.^[2] These are label facts for reference, not a recommendation, and your own schedule may differ. Your prescriber decides your dose and any change to it.

If a dose is missed, the Ozempic label says to give it as soon as possible within 5 days after the missed dose.^[1] Ask your prescriber what applies to you.

What does each semaglutide dose step look like in syringe units?

Each dose step becomes a different syringe mark at each concentration. Multiply the dose by 100 and divide by the concentration to get units on a U-100 syringe.^[7] A 0.5 mg dose is 50 units at 1 mg/mL, 20 units at 2.5 mg/mL, and 10 units at 5 mg/mL. A 2.4 mg dose is 240 units at 1 mg/mL, which is more than a 1 mL syringe holds, 96 units at 2.5 mg/mL, and 48 units at 5 mg/mL. The grid below lists the dose steps from the two labels at three common concentrations. Cells marked over need more than the 100 units a 1 mL U-100 barrel holds, so the volume exceeds one barrel. What applies to your product is a question for your pharmacist or prescriber. Use the grid to see the pattern, then enter your own vial and dose for the exact figure. The grid is arithmetic from the label steps and does not suggest that any step is right for you.

How long does a multi-dose semaglutide vial last once opened?

The FDA recommends that vials containing multiple doses of sterile medications be used within 28 days after the first use, because the risk of contamination increases after 28 days.^[4] That is a general limit for multi-dose vials, and your product may carry a different or shorter one, so read the label or ask your pharmacist. Write the date of first use on the vial. Because a pharmacy sets the strength of a compounded vial, the number of doses it holds also depends on your own dose. Divide the milligrams in the vial by the milligrams in one dose. A 10 mg vial and a 0.5 mg dose give 20 doses, but a weekly schedule would reach the 28-day limit after about four doses. Any peptide left after that date is outside the FDA advice, so ask your pharmacist how to handle the leftover instead of guessing.