Quick math example
A 5 mg vial mixed with 2 mL gives 2.5 mg/mL. A 0.25 mg dose is 0.1 mL, which equals 10 units on a U-100 syringe.
How BAC water volume changes a semaglutide draw
The water you add sets the concentration; the dose decides the draw. For a 5 mg vial: 1 mL gives 5 mg/mL (0.25 mg = 5 units), 2 mL gives 2.5 mg/mL (0.25 mg = 10 units), and 3 mL gives 1.67 mg/mL (0.25 mg = 15 units).
More water makes small doses easier to measure accurately, because the draw lands on more unit lines.
- 5 mg / 1 mL = 5 mg/mL → 0.25 mg = 5 units
- 5 mg / 2 mL = 2.5 mg/mL → 0.25 mg = 10 units
- 5 mg / 3 mL = 1.67 mg/mL → 0.25 mg = 15 units
Trade-offs when choosing BAC water for semaglutide
There is no clinically "correct" reconstitution volume — semaglutide is the same molecule at any dilution. The trade-offs are practical: readability, draw size, dead-space waste, and beyond-use window.
Smaller water volumes (concentrated): smaller draws, more peptide saved against dead-space loss per draw, but small doses land on the very bottom of a U-100 syringe where the unit lines are tight together.
Larger water volumes (diluted): larger draws, doses spread across more readable unit lines, but each draw loses slightly more product to syringe dead space, and the vial holds the same total mg in a larger fluid volume.
- More water → easier to read small doses, slightly more waste per draw
- Less water → bigger reserve, but tighter draws at starter doses
- Dead-space loss is ~0.05 mL per draw — usually negligible at moderate concentrations
How the semaglutide calculation works
The calculator first converts the vial amount from mg to mcg, then divides by the BAC water volume to find concentration. Your target dose is divided by that concentration to return mL and syringe units.
For GLP-1 compounds, small dose changes can meaningfully change the draw volume. Re-run the calculation whenever vial size, water amount, syringe type, or target dose changes.
- Concentration = vial mcg / water mL
- Dose volume = target dose mcg / concentration
- U-100 units = dose volume mL x 100
Semaglutide 5 mg vial with 2 mL example
A 5 mg semaglutide vial mixed with 2 mL gives a concentration of 2.5 mg/mL, or 2,500 mcg/mL.
A 0.25 mg dose is 250 mcg. At 2,500 mcg/mL, that dose is 0.1 mL, which equals 10 units on a U-100 syringe.
- 5 mg / 2 mL = 2.5 mg/mL
- 0.25 mg = 250 mcg
- 250 mcg / 2,500 mcg per mL = 0.1 mL = 10 U-100 units
Semaglutide 10 mg vial with 2 mL example
A 10 mg semaglutide vial mixed with 2 mL gives a concentration of 5 mg/mL, or 5,000 mcg/mL.
A 0.5 mg dose is 500 mcg. At 5,000 mcg/mL, that dose is 0.1 mL, which equals 10 U-100 units.
- 10 mg / 2 mL = 5 mg/mL
- 0.5 mg = 500 mcg
- 500 mcg / 5,000 mcg per mL = 0.1 mL = 10 U-100 units
Use with compounded or lyophilized vials
This page is intended for situations where you need to calculate a dose from a vial and diluent volume. Pre-filled commercial pens usually do not require this math.
Follow the label, pharmacy directions, and clinician instructions for storage, titration, and beyond-use dates.