GlidedoseReconstitution calculator: vial & syringe unit converter
Turn the numbers on your prescription and pharmacy label (vial strength, water added and your prescribed dose) into mL and insulin syringe units. It shows the math so you can check it.
Important: Use only the dose and mixing instructions from your prescriber or pharmacist. This tool converts the numbers you enter; it does not give medical advice. Double-check every result.
This only does arithmetic on the numbers you enter. It doesn't know your medication, your dose or your syringe.
How the conversion works
- Concentration = mg of medication in the vial ÷ mL of water added. A 5 mg vial with 2 mL of water is 2.5 mg/mL.
- Volume to draw = prescribed dose (mg) ÷ concentration. 0.25 mg ÷ 2.5 mg/mL = 0.1 mL.
- Syringe units = volume (mL) × the syringe's units per mL. U-100, U-50 and U-30 insulin syringes are all 100 units per mL (they differ only in barrel size), so 0.1 mL = 10 units. U-40 syringes are 40 units per mL, so 0.1 mL = 4 units.
- Doses per vial = total mg in the vial ÷ dose. 5 mg ÷ 0.25 mg = 20 doses.
Using a different syringe than the one your pharmacy specified is one of the most common causes of measuring errors, because the same mL reads as a different number of units. Insulin syringes are marked in units, not mg.
Worked examples (checked by hand)
| Vial & mixing | Concentration | Dose entered | mL | U-100 units | Doses per vial |
|---|---|---|---|---|---|
| Semaglutide 5 mg + 2 mL | 2.5 mg/mL | 0.25 mg | 0.10 | 10 | 20 |
| Semaglutide 5 mg + 2 mL | 2.5 mg/mL | 0.5 mg | 0.20 | 20 | 10 |
| Semaglutide 5 mg + 2 mL | 2.5 mg/mL | 1 mg | 0.40 | 40 | 5 |
| Tirzepatide 10 mg + 2 mL | 5 mg/mL | 2.5 mg | 0.50 | 50 | 4 |
| Tirzepatide 10 mg + 2 mL | 5 mg/mL | 5 mg | 1.00 | 100 | 2 |
These are arithmetic examples, not dosing recommendations. For dose steps on approved branded products, see the GLP-1 dose schedule from the official labels.
Safety notes
- Branded pens (Ozempic, Wegovy, Mounjaro, Zepbound) are pre-dosed and don't need this. Follow the pen instructions.
- The FDA has received reports of dosing errors with compounded semaglutide, including patients measuring in units instead of mL or the wrong syringe size. If anything doesn't match your label, stop and call your pharmacy.
- Only use medication dispensed by a licensed pharmacy with a prescription. Health Canada and the FDA warn against buying semaglutide or tirzepatide from unauthorized online sellers.
- Never reuse or share syringes, and record each injection so you don't double up. See missed dose rules and injection site rotation.
Sources
- FDA: dosing errors associated with compounded injectable semaglutide products
- FDA: concerns with unapproved GLP-1 drugs used for weight loss
- Health Canada: unauthorized semaglutide products may pose serious health risks
Use only the dose and mixing instructions from your prescriber or pharmacist. This tool converts the numbers you enter; it does not give medical advice. Double-check every result.
Frequently asked questions
How many units is 0.25 mg of semaglutide?
It depends entirely on how your vial was mixed. Example: a 5 mg vial mixed with 2 mL of bacteriostatic water is 2.5 mg/mL. 0.25 mg ÷ 2.5 mg/mL = 0.1 mL, which is 10 units on a U-100, U-50 or U-30 insulin syringe. If your vial has a different strength or was mixed with a different amount of water, the units change, so use the numbers on your pharmacy label.
How many units is 0.5 mg of semaglutide?
With the same 5 mg + 2 mL example (2.5 mg/mL), 0.5 mg ÷ 2.5 = 0.2 mL, or 20 units on a U-100 syringe. The vial holds 5 ÷ 0.5 = 10 doses of that size.
How many units is 2.5 mg of tirzepatide?
Example: a 10 mg vial mixed with 2 mL is 5 mg/mL. 2.5 mg ÷ 5 mg/mL = 0.5 mL, which is 50 units on a U-100 or U-50 syringe. That is more than a U-30 syringe holds. Your pharmacy label may list a different concentration.
What does U-100 mean?
U-100 insulin syringes are marked so that 100 units equals 1 mL, so 1 unit is 0.01 mL. U-50 (0.5 mL) and U-30 (0.3 mL) syringes use the same scale in a smaller barrel. U-40 syringes are scaled for 40 units per mL, so the same volume reads as fewer units.
Does this tool tell me what dose to take?
No. It only converts the dose, vial strength and water volume you enter into mL and syringe units. Your dose and mixing instructions must come from your prescriber or pharmacist.
Can I use it for research peptides?
No. Glidedose is built for people using medications prescribed to them. This converter is intended for prescription semaglutide, tirzepatide and other prescribed injectables dispensed by a licensed pharmacy.
Related guides
Week-by-week escalation for Ozempic, Wegovy, Mounjaro and Zepbound from the labels.Injection site rotation
Six-zone rotation chart, where Ozempic and Mounjaro labels say to inject, and spots to avoid.Missed a GLP-1 dose?
The 5-day, 48-hour and 4-day windows on the Ozempic, Wegovy, Mounjaro and Zepbound labels.