Semaglutide Dose Calculator: mg to Units on a U-100 Syringe

1. Type the strength the way your vial label prints it, such as 2.5 mg/mL or 2.5 mg / 0.5 mL. The calculator repeats back how it read the label. Ozempic and Wegovy pens deliver a set dose in mg, and the calculator says so if you choose a pen.
2. Enter your prescribed dose in mg.
3. Pick your syringe size: 0.3 mL, 0.5 mL or 1 mL.
4. Read the line to draw to, the mg it holds and what one unit is worth at your dose. When a dose could also be read as a tenth of itself, such as 2.5 mg and 0.25 mg, both are shown with their units so your prescription can settle it.
5. Add the mL of liquid in the vial and the date of your first draw to see how many doses you get before FDA’s 28-day discard date, and keep the vial card.

Units = semaglutide dose in mg ÷ vial concentration in mg/mL × 100. The volume in mL is the same dose ÷ the same concentration, without the × 100. The 100 comes from the syringe: a U-100 syringe is marked so that 100 units fill 1 mL, and FDA’s example of a small dose is 5 units, or 0.05 mL (FDA alert on compounded semaglutide dosing errors).

For 0.5 mg from a 2.5 mg/mL vial: 0.5 ÷ 2.5 = 0.2 mL, and 0.2 × 100 = 20 units. For 0.25 mg from a 2 mg/mL vial the answer is 12.5 units, which sits between two marks. On a syringe with 1-unit marks the calculator rounds to 13 units and shows that 13 units hold 0.26 mg, 4% more than the dose.

Each cell is the dose ÷ the concentration × 100, at four example strengths. The doses are the steps on the Ozempic and Wegovy labels (Ozempic prescribing information, section 2.2; Wegovy prescribing information, section 2.2).

A U-100 syringe holds 100 units at most. The 1 mg/mL vial that puts 0.25 mg at an easy-to-read 25 units cannot deliver 1.7 mg or more in one draw, and the 7.2 mg Wegovy step would be 144 units even at 5 mg/mL. When a refill arrives at a new strength, the vial transition calculator gives the new unit count; run the checks in switching vial concentrations before the first draw.

At 5 mg/mL, a 0.25 mg dose is 5 units, or 0.05 mL. Misreading it by one unit changes the dose by 20%, because 1 ÷ 5 = 0.2. The same one-unit slip on a 50-unit draw is 2%.

FDA’s reports include patients told to draw 5 units who drew 50, and a prescriber who meant 0.25 mg (5 units) but wrote 25 units (FDA alert on compounded semaglutide dosing errors). FDA encourages prescribers and compounders to give patients a syringe sized for the dose and to show them how to measure it.

A semaglutide vial labeled 2.5 mg / 0.5 mL holds 5 mg/mL. Typing 2.5 into the mg/mL field would double every volume, so a 0.5 mg dose would come out at 20 units instead of 10. A label that gives only a total works the same way: 10 mg in 4 mL is 2.5 mg/mL. Type both numbers as the label prints them, 2.5 mg / 0.5 mL, and the calculator does the division.

A vial you mix yourself follows the same arithmetic: 5 mg of powder in 2 mL of water is 2.5 mg/mL, and the same 5 mg in 1 mL is 5 mg/mL, which halves every unit count. Tap "Mixed it yourself? Powder + water" and enter the mg on the vial and the mL of water you added.

FDA notes that compounders supply semaglutide in various concentrations (FDA alert on compounded semaglutide dosing errors). Compounded drugs are not FDA approved, and FDA does not review them for safety, effectiveness or quality before they are marketed (FDA, concerns with unapproved GLP‑1 drugs), so enter the figure printed on the vial in your hand.

Ozempic and Wegovy both start at 0.25 mg once weekly for 4 weeks, and each later step comes after at least 4 weeks on the dose before (Ozempic and Wegovy prescribing information, section 2.2).

There is no 2.4 mg Ozempic dose. The 7.2 mg Wegovy dose comes in its own Wegovy HD pen, and the GLP‑1 dose conversion chart lists every step for each brand. The weeks after each step up are described in what to expect after an Ozempic dose increase.

Logging every dose in Pensday keeps each step’s dates straight, and its free reminders tell you when the next one is due.

Branded Ozempic and Wegovy come as pens and prefilled syringes that deliver a labeled dose in mg, so there are no units to work out (Ozempic prescribing information, section 3; Wegovy prescribing information, section 3). Wegovy also comes as a once-daily tablet; see the Wegovy pill guide. To check a draw the other way, from units back to mg, use the reverse dose calculator.