GLP-1 Dose Calculator: Convert Semaglutide & Tirzepatide mg to Units

If your compounded semaglutide or tirzepatide vial's label reads differently from what you expected, or your pharmacy just switched suppliers and the numbers don't match your old prescription, you're not imagining things. The short version: units on a syringe and milligrams of medication are two different measurements, and the number that connects them is your specific vial's concentration, which varies by compounding pharmacy. There's no single universal answer to "how many units is 2.5 mg," because it depends on what's actually in your vial.

The calculator above does the math for you in either direction: enter your dose to see the units, or enter the units you were told to draw to see the dose. Everything below explains why the conversion works the way it does, walks through the formula by hand, and answers the specific questions we hear most from patients on compounded GLP-1 medications.

Your prescription is written in milligrams (mg). That's the actual dose of medication. Your syringe, though, doesn't measure milligrams directly. A standard insulin syringe measures volume, marked in units, where 100 units equals 1 milliliter (mL) on a "U-100" syringe, the type used for essentially all compounded semaglutide and tirzepatide.

The bridge between the two is concentration: how many milligrams of medication are dissolved in each milliliter of liquid in your vial, usually printed on the label as "X mg/mL." Once you know that number, the conversion is simple arithmetic. Without it, a unit count on a syringe tells you nothing about how much medication you're actually about to inject.

This is the part that trips up most patients, and it's worth explaining plainly: compounding pharmacies aren't manufacturing a standardized, one-size-fits-all product the way a brand-name pen is. Each pharmacy prepares its own batches, and the concentration they choose to compound at is their own decision: one pharmacy might dispense semaglutide at 2.5 mg per mL, another at 5 mg per mL. Both are legitimate preparations of the same medication. Neither is "the" concentration.

That means if you've ever switched pharmacies, or a friend on the same prescribed dose tells you they draw a completely different number of units than you do, that's expected, not a sign either of you is doing it wrong. What matters is that your unit count matches your own vial's concentration, every time, including if that concentration ever changes.

The formula behind the calculator above is straightforward, and it's worth knowing even if you use the tool every time: units = (your dose in mg ÷ your vial's concentration in mg/mL) × 100.

For example, say your vial is labeled 10 mg/mL and you're prescribed a 2.5 mg dose. Divide 2.5 by 10 to get 0.25 mL, then multiply by 100 (because the syringe is U-100) to get 25 units. Change the concentration to 20 mg/mL with the same 2.5 mg dose, and the math gives you 12.5 units instead: half as much volume, for the identical dose, because the medication is twice as concentrated.

The tables in the calculator above cover the concentrations most often cited for compounded semaglutide (2.5 and 5 mg/mL) and tirzepatide (10, 17 and 20 mg/mL), matched against the standard titration doses for each medication. These are common starting points, not a guarantee of what your own pharmacy uses. The number on your vial's label always takes priority over any example on this page.