Semaglutide Peptide Calculator
Reconstituting a semaglutide research vial comes down to four numbers: the milligrams in the vial, the milliliters of bacteriostatic water you add, the dose you want, and the syringe you draw it with. This calculator turns those four inputs into an injection volume in milliliters, the exact tick mark on a U-100 insulin syringe, the vial concentration, and how many doses the vial holds. It is a math tool for informational use only: semaglutide is a prescription medicine, and any dosing decision belongs to you and your clinician.
Units are U-100 insulin syringe units: 100 units = 1 ml on any U-100 syringe. Verify every result with your clinician or pharmacist before drawing a dose.
Quick Answer
A 5 mg semaglutide vial mixed with 2 ml of bacteriostatic water gives a concentration of 2.50 mg/ml. A 0.25 mg dose is therefore 0.100 ml, which you draw to the 10.0-unit mark on any U-100 insulin syringe, and the vial holds 20.0 doses at that strength. The unit count never depends on which size syringe you use: 100 units always equals 1 ml.
Key takeaways
- Reconstitution math is three divisions: vial mg divided by water ml gives concentration, dose mg divided by concentration gives ml, and ml times 100 gives syringe units.
- A U-100 syringe measures volume, not medicine. Ten units on a 0.3 ml syringe and ten units on a 1 ml syringe are the same 0.1 ml; the barrel size only sets how much you can draw at most.
- Brand-name semaglutide (Ozempic, Wegovy) comes pre-mixed in pens, so this calculator is for compounded or research vials where you set the concentration yourself. It is not affiliated with Novo Nordisk.
- Semaglutide is prescription-only. The FDA has logged dosing errors, some requiring hospitalization, from patients miscalculating compounded semaglutide doses, so every result here must be confirmed with a clinician.
- Quick Answer
- How to use the semaglutide peptide calculator
- The reconstitution formula, step by step
- Worked example: 5 mg vial, 2 ml water, 0.25 mg dose
- What competing calculators miss
- Syringe sizes: what the barrel really decides
- Brand-name pens versus compounded vials: which one is this for?
- Safety: the part no calculator can do for you
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the semaglutide peptide calculator
Enter your vial size, the water you add, and your prescribed dose, then click Calculate. The tool shows the syringe units to draw, the injection volume, the concentration, and the number of doses in the vial.
- Enter the vial size in mg. Read it off the vial label. 5 mg is pre-filled as the worked example.
- Enter the bacteriostatic water in ml. This is the volume you mix in, not the vial’s capacity. 2 ml is pre-filled.
- Enter your prescribed dose in mg. This must come from your clinician, never from guesswork. 0.25 mg, the standard semaglutide starting dose, is pre-filled.
- Pick your syringe type. The unit math does not change with it, as the formula section explains, but the tool now warns if the draw exceeds the barrel you picked: a 0.3 ml syringe holds at most 30 units, a 0.5 ml syringe holds 50, and a 1 ml syringe holds 100.
- Click Calculate and read the draw. The headline result is the unit mark on your U-100 syringe. Results stay hidden until you calculate, and you can copy them for your records.
For the general dilution arithmetic behind any peptide, the chemical dilution calculator covers the same concentration logic, and if your dose is written in micrograms rather than milligrams, the mg to IU calculator explains why there is no generic mg-to-unit conversion without a concentration.
The reconstitution formula, step by step
Concentration (mg/ml) = vial size (mg) ÷ water added (ml). Injection volume (ml) = desired dose (mg) ÷ concentration. Syringe units = injection volume × 100. Doses per vial = vial size ÷ desired dose. Each line feeds the next, and every value the tool reports comes from these four lines.
Injection volume = dose (mg) ÷ concentration (mg/ml)
Syringe units = injection volume (ml) × 100 (U-100: 100 units = 1 ml)
Doses per vial = vial size (mg) ÷ dose (mg)
A math error this page fixes
The previous version of this tool computed syringe units as injection volume × (syringe size × 100). With the default 0.3 ml syringe selected, a 0.25 mg dose from a 5 mg / 2 ml vial showed 3.0 units instead of the correct 10.0 units: a 70% underdose on screen. That is wrong because U-100 means 100 units per milliliter on every U-100 syringe; a 0.3 ml barrel simply holds 30 units at most. The fixed formula multiplies by 100 regardless of barrel size, which matches the tool’s own written formula and every competitor calculator checked. The syringe-type selector is preserved in the card but no longer changes the unit count; it only records which barrel you draw with.
One more thing the syringe cannot tell you: units are not milligrams. Ten units of a 2.5 mg/ml mix is 0.25 mg; ten units of a 5 mg/ml mix is 0.5 mg. The milligram content of your draw depends entirely on the concentration you created, which is why the tool reports both numbers side by side. If your prescription is written in micrograms rather than milligrams, the dose conversion calculator handles the mg to mcg step before you enter the dose here.
Worked example: 5 mg vial, 2 ml water, 0.25 mg dose
The calculator is pre-filled with the most common starter setup. Here is the arithmetic it runs:
Click Calculate with the pre-filled values and you get exactly these figures: 10.0 units, 0.100 ml, 2.50 mg/ml, 20.0 doses. The most-used dose steps for this exact mix are worth memorizing, and each row below is a real run of this calculator:
| Dose (mg) | Injection volume (ml) | Draw to (U-100 units) | Doses per 5 mg vial |
|---|---|---|---|
| 0.25 (starter) | 0.100 | 10.0 | 20.0 |
| 0.5 | 0.200 | 20.0 | 10.0 |
| 1.0 | 0.400 | 40.0 | 5.0 |
| 1.7 | 0.680 | 68.0 | 2.9 |
| 2.4 | 0.960 | 96.0 | 2.1 |
Practical dose counts run slightly below the arithmetic because of syringe dead space and because reconstituted vials should be discarded after 28 days even if liquid remains, which is the standard beyond-use guidance the FDA references for compounded injectables. Never stretch a vial past your compounder’s discard date to chase the last dose.
What competing calculators miss
Peptide calculators cluster into three groups, each with a blind spot:
- Generic reconstitution tools (AI Peps, OptiPin, RealPeptideCalculator): solid math and clean unit readouts, but built for every peptide at once. None anchors the worked examples to semaglutide’s actual clinical dose ladder, so users must map BPC-157-style microgram examples onto milligram GLP-1 dosing themselves.
- Guide-plus-calculator pages (PeptideDeck, GLP-1 Calculator): excellent semaglutide-specific tables, but the calculator and the article live in separate mental boxes; several bury the unit readout below long guides and none explains why barrel size does not change the math.
- Unit-converter pages (PeptideClock, PeptideDosage): strong on syringe reading technique, but they answer “how to read a syringe” rather than “what to draw,” leaving the reconstitution division to the user.
- The gap this page fills: semaglutide-specific dosing in one place, the syringe-size error that lived in this very tool called out and fixed with proof, a dose ladder table generated from the corrected math, and the brand-versus-compounded distinction that decides whether you need this calculator at all.
Syringe sizes: what the barrel really decides
Your U-100 syringe size decides the largest dose you can draw in one pull, and how finely you can read small doses. It never changes how many units a given volume equals.
Choose the smallest barrel that comfortably holds your dose: finer tick spacing means more accurate small draws. If the tool’s unit figure ever exceeds your syringe’s maximum, that is a signal to check the dose with your prescriber, not to split it across two draws on your own initiative.
Brand-name pens versus compounded vials: which one is this for?
This calculator is for vials where you set the concentration, not for brand-name pens. The distinction matters because it decides whether any math is needed at all.
Brand-name pens (no math needed)
- Ozempic (Novo Nordisk): pre-filled pens delivering 0.25, 0.5, 1 or 2 mg once weekly for type 2 diabetes, per the FDA-approved label.
- Wegovy (Novo Nordisk): pre-filled pens up to 2.4 mg once weekly for chronic weight management, FDA-approved in 2021.
- Rybelsus: the same molecule as a daily tablet, not an injection at all.
- You dial the dose; the pen meters it. A reconstitution calculator has nothing to compute.
Compounded or research vials (this calculator)
- Lyophilized powder vials where you add the bacteriostatic water and set the concentration.
- Unit marks must be computed from your mix, which is exactly what the tool above does.
- Compounded drugs are not FDA-approved products and skip premarket review; the FDA urges using them only when an approved drug cannot meet the medical need.
- Salt forms sold by some compounders (semaglutide sodium, semaglutide acetate) are different active ingredients from the approved drug, per the FDA.
Calculator Zilo is not affiliated with Novo Nordisk. If your prescription is for a brand-name pen, follow the pen’s instructions for use; if it is for a compounded vial, this calculator handles the arithmetic while your clinician handles the dosing decisions. For dose schedules and titration steps rather than vial math, see the semaglutide dosage calculator, which covers the clinical dose ladder this page deliberately does not duplicate.
Safety: the part no calculator can do for you
Correct arithmetic is necessary but not sufficient. Semaglutide carries a boxed warning for thyroid C-cell tumors seen in rodents, and the label lists pancreatitis, gallbladder disease and gastrointestinal effects among its risks, which is why it stays prescription-only. The FDA’s concern page for unapproved GLP-1 drugs reports dosing errors with compounded semaglutide, some requiring hospitalization, when patients measured or administered the wrong dose; some overdoses reached many times the intended amount. Treat every number on this page as a draft to verify: confirm the vial strength, the water volume, the prescribed dose and the drawn units with your clinician or pharmacist, use a new sterile needle and syringe for each injection, and store reconstituted vials refrigerated per your compounder’s instructions. If a dose ever looks surprising, stop and ask before injecting.
Frequently asked questions
Divide the vial milligrams by the milliliters of bacteriostatic water to get the concentration, divide your dose by that concentration to get the injection volume in ml, then multiply the ml by 100 for U-100 syringe units. For a 5 mg vial with 2 ml water and a 0.25 mg dose: 2.50 mg/ml, 0.100 ml, 10.0 units.
No. On every U-100 insulin syringe, 100 units equals 1 ml, whether the barrel holds 0.3 ml, 0.5 ml or 1 ml. The barrel size only sets the maximum you can draw: 30, 50 or 100 units. The tool now warns if your draw exceeds the barrel you picked, without changing the unit math. A previous version of this calculator multiplied by the syringe size and showed 3.0 units where 10.0 was correct; that error is now fixed.
It depends on your mix. With the standard 5 mg vial plus 2 ml bacteriostatic water (2.50 mg/ml), 0.25 mg is 10.0 units. With a more dilute mix, such as 5 mg in 5 ml (1 mg/ml), the same 0.25 mg dose is 25 units. Units measure volume, not milligrams, so always compute from your own concentration.
Bacteriostatic water is sterile water containing a small amount of benzyl alcohol that inhibits bacterial growth, which makes it the standard diluent for multi-dose peptide vials. It is different from plain sterile water, which has no preservative. Use only the diluent your clinician or compounding pharmacy specifies.
Divide 5 mg by your dose: 20 doses at 0.25 mg, 10 at 0.5 mg, 5 at 1 mg. In practice you will get slightly fewer because of syringe dead space, and reconstituted vials should be discarded after 28 days even if liquid remains, so a low dose does not always mean the full arithmetic number of usable doses.
No. Ozempic and Wegovy are pre-filled pens where you dial the dose and the pen meters it: no reconstitution math is needed. This calculator is for compounded or research vials where you add the water and set the concentration yourself. Calculator Zilo is not affiliated with Novo Nordisk, the maker of both brands.
No. Dose changes, including titration steps, must be approved by your prescriber. The FDA has reported hospitalizations from dosing errors with compounded semaglutide, including overdoses many times the intended amount. This calculator does arithmetic only and never recommends a dose.
Refrigerate it and follow your compounding pharmacy’s storage and discard instructions; the FDA references a 28-day discard window for compounded injectables even when medicine remains. Do not use a vial that arrived warm without adequate cooling, looks cloudy or discolored, and use a new sterile needle and syringe for every injection.
The FDA-approved label carries a boxed warning for thyroid C-cell tumors observed in rodents, and lists pancreatitis, gallbladder disease, kidney injury and severe gastrointestinal effects among its warnings. Common side effects include nausea, vomiting, diarrhea, abdominal pain and constipation. Discuss your personal and family medical history with your clinician before starting.
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References
- U.S. National Library of Medicine, DailyMed. Ozempic (semaglutide) injection, FDA-approved drug label: dosage forms and strengths (0.25 to 2 mg pens; 0.68, 1.34 and 2.68 mg/mL), dosing schedule, boxed warning for thyroid C-cell tumors. Accessed October 23, 2026.
- U.S. Food and Drug Administration. FDA’s Concerns with Unapproved GLP-1 Drugs Used for Weight Loss: dosing errors with compounded semaglutide including hospitalizations, salt forms, and the 28-day discard guidance. Accessed October 23, 2026.
- U.S. Food and Drug Administration (via PR Newswire). FDA Approves New Drug Treatment for Chronic Weight Management, First Since 2014: Wegovy (semaglutide) 2.4 mg once-weekly approval for chronic weight management. Accessed October 23, 2026.
- U.S. National Library of Medicine, MedlinePlus. Semaglutide Injection: Drug Information: approved uses, thyroid tumor warning, and patient guidance. Accessed October 23, 2026.
- StatPearls Publishing (via NCBI Bookshelf). Obesity Medications: Evidence-Based Management: semaglutide as a GLP-1 receptor agonist, indications and weight effects. Accessed October 23, 2026.
- Carvalho, M. et al. Semaglutide as a GLP-1 Agonist: A Breakthrough in Obesity Treatment, peer-reviewed review: mechanism, half-life of about one week, and the 0.25 to 2.4 mg weekly dose range. Accessed October 23, 2026.
- DosePlot. Insulin Syringe Units Explained: U-100 to mL Conversion: U-100 means 100 units per mL on any U-100 syringe; 0.1 ml equals 10 units. Accessed October 23, 2026.
- PeptideDosage. How to Read a U-100 Insulin Syringe: 0.3, 0.5 and 1.0 ml barrels hold 30, 50 and 100 units respectively; 1 unit equals 0.01 ml. Accessed October 23, 2026.
- Novo Nordisk (via NovoMedLink). Ozempic FAQs: packaging and administration: pen configurations (2 mg/3 mL, 4 mg/3 mL, 8 mg/3 mL) and once-weekly dosing. Accessed October 23, 2026.
- GLP-1.app. What Is Semaglutide?: GLP-1 mechanism, brands (Ozempic, Wegovy, Rybelsus), half-life of about one week. Accessed October 23, 2026.