Short answer: Divide the dose in mg by the strength on the vial in mg/mL, then multiply by 100. That gives units on a U-100 insulin syringe. At 2.5 mg/mL, 0.25 mg of semaglutide is 10 units; at 10 mg/mL, 2.5 mg of tirzepatide is 25 units. A different vial strength gives a different number.
Compounded semaglutide and tirzepatide usually come already in solution, in multi-dose vials, with instructions in syringe units. Those units only make sense together with the vial strength. These pages turn every dose step named in the FDA labels for Ozempic, Wegovy, Mounjaro and Zepbound into units at each common compounded strength, show how many doses a vial holds, and quote the label schedules with citations.
FDA-approved pens are dosed in mg and need none of this math. Compounded products are not FDA approved (FDA). Nothing here is a dose recommendation. Not personalized advice; confirm your dose, in mg and in units, with your prescriber or the dispensing pharmacy.
If you add bacteriostatic water to the vial yourself, the strength depends on how much water you add. Use the reconstitution calculator or the semaglutide and tirzepatide powder vial guides instead.