Guide
GLP-1 dosing guide: how to calculate units from mg and mg/mL
Your prescription is written in milligrams (mg), but your syringe is marked in units. To get from one to the other you also need your vial concentration in mg/mL. Here is how it works, with units charts for compounded semaglutide and tirzepatide.
Why the math trips people up
Brand-name pens are dosed with the pen itself. A compounded vial is different: you measure your own dose with a U-100 insulin syringe. To get it right you need three things: your dose in mg, your vial's concentration in mg/mL, and the syringe you are using.
The terms you need
| Term | What it means | Example |
|---|---|---|
| Vial volume (mL) | The total liquid in the vial. Vials are small and can look partly empty: 2.5 mL is about half a teaspoon. | 3 mL |
| Concentration (mg/mL) | How much medication is in each mL of liquid | 10 mg/mL |
| Total medication (mg) | Concentration × vial volume | 10 mg/mL × 3 mL = 30 mg |
| Dose (mg) | How much your prescriber wants you to take each time. It is on your prescription, not the vial. | 5 mg |
| Units | The printed lines on a U-100 insulin syringe. 100 units = 1 mL. | 50 units |
The key fact: on a U-100 insulin syringe, 1 unit = 0.01 mL. Units measure liquid, not medication, so the same 20 units can hold very different doses depending on the vial.
Reading tricky labels
- Two ingredients. A label like "Tirzepatide/Niacinamide 8 mg/2 mg/mL" lists each ingredient in order. Use only the GLP-1 number, here 8 mg/mL.
- Written per 0.5 mL. "10 mg/0.5 mL" means 20 mg in every mL. Double it before you calculate.
- cc is not units. 1 cc = 1 mL = 100 units. Syringe sizes are often sold in cc: a 0.5 cc syringe holds 50 units.
More label formats are in Switching pharmacies and How to read your prescription.
How to convert mg to units
Divide your dose by the concentration to get mL, then multiply by 100.
| Example | Step 1: mL | Step 2: units |
|---|---|---|
| Semaglutide 0.25 mg, 2.5 mg/mL vial | 0.25 ÷ 2.5 = 0.1 mL | 0.1 × 100 = 10 units |
| Semaglutide 1 mg, 5 mg/mL vial | 1 ÷ 5 = 0.2 mL | 0.2 × 100 = 20 units |
| Tirzepatide 5 mg, 10 mg/mL vial | 5 ÷ 10 = 0.5 mL | 0.5 × 100 = 50 units |
Going the other way: units to mg
To check a unit count, reverse it: dose in mg = (units ÷ 100) × concentration. For example, 30 units of a 2.5 mg/mL vial is 0.3 mL × 2.5 = 0.75 mg.
GLP-1 units charts
Find your dose and your vial's concentration to see the calculated units on a U-100 syringe. Always confirm the concentration printed on your own vial.
Semaglutide
| Dose | 2.5 mg/mL vial | 5 mg/mL vial |
|---|---|---|
| 0.25 mg | 10 units | 5 units |
| 0.5 mg | 20 units | 10 units |
| 1 mg | 40 units | 20 units |
| 1.7 mg | 68 units | 34 units |
| 2.4 mg | 96 units | 48 units |
Tirzepatide
| Dose | 10 mg/mL vial | 20 mg/mL vial |
|---|---|---|
| 2.5 mg | 25 units | 12.5 units* |
| 5 mg | 50 units | 25 units |
| 7.5 mg | 75 units | 37.5 units* |
| 10 mg | 100 units (a full 1 mL syringe) | 50 units |
| 12.5 mg | 125 units** | 62.5 units* |
| 15 mg | 150 units** | 75 units |
Doses shown are examples, not a dosing schedule. Your prescriber sets your dose. * Half units fall between printed lines on most syringes: ask your pharmacist how to measure them. ** More than a 1 mL syringe holds: ask your pharmacist or prescriber, and do not split a dose on your own.
Common mistakes to avoid
- Rushing. Write your dose and your vial's concentration on paper, do the math, and pause before you draw.
- Treating units as mg. "10 units" and "10 mg" are very different. Units are a volume mark, not a dose.
- Misreading a label written per 0.5 mL. "5 mg/0.5 mL" is 10 mg/mL. Using the wrong number doubles or halves the dose.
- Assuming a new vial matches the old one. Check the concentration on every new vial. If it changed, your units change too.
- Using the wrong syringe. These numbers are for U-100 insulin syringes. A 0.3 mL or 0.5 mL U-100 syringe uses the same units with fewer lines. Never use a U-40 syringe with these numbers.
- Running low and guessing. If a vial does not have enough left for your full dose, ask your pharmacist what to do. Never mix the contents of two vials.
- Taking extra doses. Take only the dose and schedule your prescriber gave you.
Contact your prescriber or pharmacist. If you feel unwell, call Poison Control at 1-800-222-1222, and call 911 in an emergency.
Check your numbers. Enter your vial concentration, your prescribed dose and your syringe, and DoseCompa shows the calculated units and where they fall on your syringe's printed lines.
Open the calculatorQuestions
How many units is 0.25 mg of semaglutide?
It depends on your vial. At 2.5 mg/mL, 0.25 mg is 10 units. At 5 mg/mL, it is 5 units.
How many units is 2.5 mg of tirzepatide?
At 10 mg/mL, 2.5 mg is 25 units. At 20 mg/mL, it is 12.5 units, which falls between the printed lines of most syringes, so ask your pharmacist how to measure it.
How many mL is 1 unit on an insulin syringe?
On a U-100 insulin syringe, 1 unit is 0.01 mL, so 100 units is 1 mL.
Is a unit the same as a cc?
No. 1 cc is 1 mL, which is 100 units on a U-100 syringe.
Why did my units change with a new vial?
Your new vial probably has a different concentration. The same mg dose then takes a different volume, so the units change.
How much medication is in my vial?
Multiply the concentration by the vial volume. A 3 mL vial at 10 mg/mL holds 30 mg in total.
What do I need before asking someone about my dose?
Your medication, your vial's concentration, your prescribed dose in mg and the syringe you use. Without the concentration, no one can tell you your units.
Does this replace my prescriber's instructions?
No. Use this guide and the calculator to understand and double-check your numbers. Your prescriber sets your dose, and your pharmacist can explain your label.