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How-to · reconstitution
Put 2 mL of bacteriostatic water into the 2 mg Semaglutide vial. That makes 1.00 mg/mL. A 0.25 mg dose is then 25.0 units on a U-100 syringe.
That volume is the one that lands the draw on a syringe line, so the reading can be checked by eye. More water makes a weaker mix and a bigger draw. Less water makes a stronger mix and a smaller one. The amount of Semaglutide in the glass never changes. Only the number of marks it takes does.
Semaglutide is the drug in Wegovy, Ozempic and Rybelsus. It copies a gut hormone called GLP-1, which helps control appetite and blood sugar.
| Water added | Concentration | Per U-100 unit | Example: 0.25 mg = |
|---|---|---|---|
| 1 mL | 2.00 mg/mL | 20 mcg | 12.5 units |
| 2 mL | 1.00 mg/mL | 10 mcg | 25.0 units |
Straight arithmetic: concentration = 2 mg ÷ water, and 1 U-100 unit = 0.01 mL. The example column shows the math at 0.25 mg; it is not a dose recommendation.
Which volume to use is a practical choice rather than a dose. Pick the one that puts your draw somewhere you can actually read it on the syringe. The flags in the last column mark where that fails. “Hard to measure” means the draw is too small to judge by eye. “Won’t fit” means it is bigger than one U-100 syringe holds.
The table above uses one worked example. These are the published quantities, converted into marks on a U-100 barrel at each water volume for a 2 mg vial. Where a quantity was never studied by injection, the row says so.
0.25 mg once weekly for 4 weeks, under the skin.
| Water added | Concentration | Draw |
|---|---|---|
| 1 mL | 2.00 mg/mL | 12.5 units |
| 2 mL | 1.00 mg/mL | 25.0 units |
FDA labelWegovy (semaglutide) — FDA-approved Prescribing Information (DailyMed) · retrieved 2026-08-20
1.7–2.4 mg once weekly, under the skin.
| Water added | Concentration | Draw, low to high |
|---|---|---|
| 1 mL | 2.00 mg/mL | 85.0 to 120.0 unitswon’t fit |
| 2 mL | 1.00 mg/mL | 170.0 to 240.0 unitswon’t fit |
FDA labelWegovy (semaglutide) — FDA-approved Prescribing Information (DailyMed) · retrieved 2026-08-20
At the worked amount, the vial contains eight doses while the stated storage window covers four. Even the smallest documented semaglutide vial can outlast the opening schedule.
The schedule opens at a quarter of a milligram, and vials are sold in whole milligrams. So any vial holds many weeks of opening doses, while a mixed vial keeps for a few.
The mismatch is structural rather than a purchasing error. It is worth knowing because it is the same on every semaglutide vial size, and it gets worse as the vial gets bigger.
The larger listed volume gives a whole number of units. The smaller one puts the draw on a half-mark that no printed line matches.
At this draw size half a unit is a real share of the dose, so the choice between the two volumes is not cosmetic here.
Read against the label’s maintenance amounts, this vial holds about one dose rather than eight. The over-supply becomes an under-supply in the same glass.
So these pages are worth reading by vial size and current dose together. Picking a vial once and assuming it keeps meaning the same thing is what goes wrong.
The table shows the offered water volumes. The calculator does the same arithmetic for any volume and any syringe, and shows its working line by line.
Open the Semaglutide calculator →The arithmetic on this page is only half the question. These are the pages that carry the other half.