Tools
Semaglutide reconstitution calculator
Reviewed September 2026
Quick answer
Divide the milligrams in the vial by the milliliters of water added: a 5 mg vial with 2 mL is 2.5 mg/mL. Then divide your dose by that and multiply by 100 for the mark on a U-100 syringe, so 0.25 mg at 2.5 mg/mL is 10 units. Semaglutide doses are small, and the difference between 5 units and 50 is one decimal place, which is why the water volume and the dose must come from your pharmacy label and your prescriber, not from a chart.
Your vial and your instructions
The total printed on the vial’s label, such as 10 mg. Not the dose, and not a per-mL figure.
The volume your pharmacy or prescriber told you to add. This tool does not pick it.
The number your prescriber set. Leave it empty to see only the concentration.
Concentration after mixing
Enter the milligrams on the vial and the milliliters of water added. The concentration appears here, and the syringe mark too if you add your dose.
Arithmetic only. It assumes the whole volume of water went into the vial and the powder fully dissolved. If your vial’s label or your prescriber’s instructions give a different figure, theirs is the one to follow.
How much bacteriostatic water for a 5 mg vial?
Whatever the pharmacy or prescriber specified. The table shows why that number matters so much: double the water and every mark on the syringe doubles with it, while the milligrams in each dose stay the same.
| Vial | + 1 mL | + 2 mL | + 4 mL |
|---|---|---|---|
| 2 mg | 2 mg/mL | 1 mg/mL | 0.5 mg/mL |
| 2.5 mg | 2.5 mg/mL | 1.25 mg/mL | 0.63 mg/mL |
| 5 mg | 5 mg/mL | 2.5 mg/mL | 1.25 mg/mL |
| 10 mg | 10 mg/mL | 5 mg/mL | 2.5 mg/mL |
Units for each Wegovy dose step
The rows are the dose steps in the Wegovy label; the columns are example strengths, because each compounding pharmacy sets its own. At 1 mg/mL the two highest steps will not fit in a 1 mL syringe at all. At 5 mg/mL the first step is 5 units, a short distance on the barrel to read correctly.2
| Dose | 1 mg/mL | 2.5 mg/mL | 5 mg/mL |
|---|---|---|---|
| 0.25 mg | 25 units | 10 units | 5 units |
| 0.5 mg | 50 units | 20 units | 10 units |
| 1 mg | 100 units | 40 units | 20 units |
| 1.7 mg | over 1 mL | 68 units | 34 units |
| 2.4 mg | over 1 mL | 96 units | 48 units |
Know your concentration already? Use the dose-in-units tool, or read semaglutide dosage in units for the reasoning.
Pens have no mixing step; vials do
Wegovy comes as a clear, ready-made solution in single-dose pens, from 0.25 mg in 0.5 mL to 7.2 mg in 0.75 mL for Wegovy HD, plus a four-dose FlexTouch pen. The dose is set by the pen, so there is nothing to dissolve and nothing to count on a syringe.2
A compounded multiple-dose vial moves that job to you. FDA’s alert asks prescribers and compounders to supply the right syringe size and to show patients how to measure the dose, and tells prescribers who are unsure to call the compounder about the calculation. The same advice holds for anyone using this page: confirm the concentration and the mark with the pharmacy before the first dose from a new vial.1
A vial sold as a research chemical is a different product, and FDA calls it one of “unknown quality.”3 What FDA has said about research vials →
Questions
- How much bacteriostatic water do you add to a 5 mg vial of semaglutide?
- The amount on your pharmacy's label or in your prescriber's instructions. The volume decides the concentration, so it is not a number to take from a chart. The arithmetic for a 5 mg vial: 1 mL makes 5 mg/mL, 2 mL makes 2.5 mg/mL and 4 mL makes 1.25 mg/mL.
- Why does adding more water change the number of units?
- More water spreads the same milligrams through more liquid, so each unit on the syringe carries less drug and the same dose takes more units. Doubling the water doubles every mark. The dose in milligrams does not change, which is why the volume has to match your pharmacy's instructions exactly.
- How many mg is 10 units of semaglutide?
- Ten units is 0.1 mL. Multiply by your vial's concentration: 0.25 mg at 2.5 mg/mL, 0.5 mg at 5 mg/mL, 0.1 mg at 1 mg/mL. Without the concentration printed on your label, a number of units has no milligram answer.
- Is semaglutide sold as a powder legal?
- Not when it is sold “for research purposes” or “not for human consumption.” FDA says it has warned companies that illegally sold semaglutide that way, and urges consumers not to buy these products, which are of unknown quality. Wegovy and Ozempic are supplied as ready-to-use solutions in pens.
Sources
- FDA drug safety communication, 'FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products', content current as of 07/26/2024
- FDA prescribing information for WEGOVY (semaglutide), section 3, Dosage Forms and Strengths, revision 6/2026 DailyMed
- FDA, 'FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss', content current as of 09/01/2026 FDA