OstinUnits to mg calculator
For compounded tirzepatide or semaglutide drawn from a vial with an insulin syringe.
Change either dose and the other updates. This converts numbers only: always follow the dose your prescriber gave you and check with your pharmacist if anything doesn't match.
How it works
Three numbers decide it: the dose in mg, the vial's strength in mg per mL, and the syringe. mL = mg ÷ strength, and on a U-100 syringe units = mL × 100 (on a U-40 syringe, × 40).
Example: 2.5 mg from a 10 mg/mL vial is 2.5 ÷ 10 = 0.25 mL, which is 25 units on a U-100 syringe.
Reading the vial label
The strength is written as mg/mL, for example 10 mg/mL. Compounded vials sometimes list two or three numbers, such as 10/2.5 mg/mL; the first is usually the GLP-1 and the rest are added ingredients like B12 or glycine. If you're not sure, ask the pharmacy that filled it.
U-100 and U-40 aren't interchangeable
A U-40 syringe holds 2.5 times as much medicine per unit marking as a U-100 syringe. 20 units on one is a different dose from 20 units on the other, so always use the units for the syringe you actually have.
Quick reference (U-100 syringe)
| Dose | 2.5 mg/mL | 5 mg/mL | 10 mg/mL | 20 mg/mL |
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Let your iPhone do the math
Ostin tracks your shots, dose steps and site rotation, shows each dose in units and mL for your vial and syringe, and reminds you on shot day. No account, no subscription.
Join the free betaFor iPhone, through Apple's TestFlight app; spots are limited.
More tools: Vial calculator · Protein goal · Site rotation