Understanding the U-100 Syringe
A U-100 insulin syringe is graduated such that 100 units = 1 mL. So one "unit" mark on the syringe = 0.01 mL. The maths is straightforward:
Concentration (mg/mL) = vial mg ÷ recon volume mL
Volume per dose (mL) = prescribed mg ÷ concentration
Units on U-100 syringe = volume mL × 100
Worked Example
You have a 5 mg vial of semaglutide, reconstituted with 2 mL of bacteriostatic water. Your prescription says 0.25 mg/week:
- Concentration = 5 ÷ 2 = 2.5 mg/mL
- Volume per dose = 0.25 ÷ 2.5 = 0.10 mL
- Units on U-100 = 0.10 × 100 = 10 units
- Doses per vial = 5 ÷ 0.25 = 20 doses
Semaglutide mg → Units Quick Reference
At the worked-example concentration of 2.5 mg/mL (a 5 mg vial in 2 mL), each standard semaglutide dose converts to units on a U-100 syringe as follows. Your own concentration may differ — always recalculate for your vial.
| Dose | Volume | Units (U-100) |
|---|---|---|
| 0.25 mg | 0.10 mL | 10 units |
| 0.5 mg | 0.20 mL | 20 units |
| 1.0 mg | 0.40 mL | 40 units |
| 1.7 mg | 0.68 mL | 68 units |
| 2.4 mg | 0.96 mL | 96 units |
Standard Semaglutide Titration (Wegovy)
FDA-approved escalation, dose increased every 4 weeks:
- Weeks 1–4: 0.25 mg/week
- Weeks 5–8: 0.50 mg/week
- Weeks 9–12: 1.0 mg/week
- Weeks 13–16: 1.7 mg/week
- Week 17+: 2.4 mg/week maintenance (or 7.2 mg Wegovy HD if escalated further)
Standard Tirzepatide Titration (Mounjaro / Zepbound)
- Weeks 1–4: 2.5 mg/week
- Weeks 5–8: 5.0 mg/week
- Weeks 9–12: 7.5 mg/week
- Weeks 13–16: 10 mg/week
- Weeks 17–20: 12.5 mg/week
- Week 21+: 15 mg/week maintenance
Slower Titration to Reduce Side Effects
If nausea, vomiting or constipation are severe, many clinicians extend each dose level to 6–8 weeks before escalating. Tolerance generally improves with time. Dropping to the previous dose for 2–4 weeks is a valid recovery move — just communicate with your prescriber.
Storage & Handling
- Store reconstituted vials refrigerated (2–8°C / 36–46°F)
- Use within 28 days of reconstitution (semaglutide); confirm BUD with your compounder
- Do not freeze; if frozen, discard
- Inspect before each draw — discard if cloudy, discoloured or contains particles
Frequently Asked Questions
How do I convert mg to units on a U-100 syringe? A U-100 insulin syringe is graduated for 100 units = 1 mL. So Units = (Dose mg ÷ Vial concentration mg per mL) × 100. Example: a 5 mg vial reconstituted in 2 mL gives 2.5 mg/mL, so a 0.25 mg dose = 0.10 mL = 10 units on the syringe.
What is the standard semaglutide titration schedule? Standard FDA-approved titration for Wegovy: weeks 1–4 = 0.25 mg/week, weeks 5–8 = 0.5 mg, weeks 9–12 = 1.0 mg, weeks 13–16 = 1.7 mg, week 17+ = 2.4 mg maintenance. Slower escalation (8 weeks per step) reduces nausea. Wegovy HD (7.2 mg) titrates to a higher maintenance dose once 2.4 mg tolerance is established.
What is the tirzepatide titration schedule? Standard Mounjaro/Zepbound titration: weeks 1–4 = 2.5 mg/week, weeks 5–8 = 5.0 mg, weeks 9–12 = 7.5 mg, weeks 13–16 = 10 mg, weeks 17–20 = 12.5 mg, week 21+ = 15 mg maintenance. Many clinicians stay at the lowest tolerated dose that is still producing weight loss, to minimise side effects and cost.
How long does semaglutide last in the body? Semaglutide has a half-life of about 7 days, so it is dosed once weekly. Steady-state plasma levels are reached after about 4–5 weeks (5 half-lives). Tirzepatide has a similar 5-day half-life and is also dosed weekly. Missing one dose drops levels meaningfully — take it as soon as remembered if within 5 days of the missed dose, otherwise skip it and resume on the next scheduled day.
What is bacteriostatic water and why is it used to reconstitute? Bacteriostatic water (BAC water) is sterile water containing 0.9% benzyl alcohol, which suppresses bacterial growth and lets a multi-dose vial be used over several weeks. Lyophilised (freeze-dried) compounded semaglutide and tirzepatide arrive as a powder and must be reconstituted before use; the volume of water you add sets the final concentration and therefore the units you draw. Always use the volume specified by your compounding pharmacy and confirm it against your vial label.
Is this calculator safe to use for compounded vials? It does the maths correctly — but you must verify the actual concentration on your own vial label and confirm the calculation with your prescriber or pharmacist before injecting. Compounded GLP-1s carry additional risks of contamination, mis-dosing and counterfeit products. The FDA has issued warnings about compounded semaglutide and tirzepatide. Brand-name Wegovy, Ozempic, Mounjaro and Zepbound pens have built-in dose dials and are safer where available.
Last reviewed: June 2026. Educational maths tool only — not medical advice and not a dosing recommendation. Always confirm your concentration, dose and titration with a licensed prescriber and pharmacist before injecting.