The math
mcg, mg, units and mL: the GLP-1 conversion guide
A GLP-1 dose is written in milligrams. An insulin syringe is marked in units. Getting from one to the other is a single calculation, and it is the exact spot where people second-guess themselves. Here is the whole thing, worked out.
This is unit math only. It cannot tell you the right dose, and it assumes your product is exactly what its label says - which is not guaranteed for compounded or research-grade vials. Verify every setup against your own vial and a licensed provider.
Three quantities, and why people mix them up
The confusion comes from treating a dose and a syringe mark as the same thing. They are not.
Milligrams (mg) and micrograms (mcg): the amount of drug
A mass. 1 mg = 1000 mcg. This is what a dose is quoted in.
Millilitres (mL): the amount of liquid
A volume. This is how much fluid you actually draw into the syringe.
Units: marks on the syringe
A scale, not a drug amount. On a U-100 insulin syringe, 100 units is 1 mL, so 1 unit is 0.01 mL. Units measure volume, not milligrams.
The formula
Everything runs off the concentration you create when you add water to the vial. Three lines get you all the way to units:
| Concentration | = vial mg / water mL |
| Volume to draw | = dose mg / concentration |
| Units (U-100) | = volume mL x 100 |
If your dose is in micrograms, divide by 1000 first to get milligrams, then continue.
Worked examples
The same dose gives a different unit count depending on how much water you used, so these numbers only hold for the exact mixing shown.
| Vial | Water | Concentration | Dose | Draw | Units (U-100) |
|---|---|---|---|---|---|
| 10 mg | 2 mL | 5 mg/mL | 2.5 mg | 0.5 mL | 50 units |
| 5 mg | 2 mL | 2.5 mg/mL | 0.25 mg | 0.1 mL | 10 units |
| 5 mg | 2 mL | 2.5 mg/mL | 0.5 mg | 0.2 mL | 20 units |
Take the first row. A 10 mg vial dissolved in 2 mL of water is 10 / 2 = 5 mg per mL. A 2.5 mg dose is 2.5 / 5 = 0.5 mL. On a U-100 syringe that is 0.5 x 100 = 50 units. Change the water to 1 mL and the concentration doubles to 10 mg/mL, so the same 2.5 mg dose becomes 0.25 mL, or 25 units. The water volume is the lever.
Questions people ask
How many units is a 2.5 mg tirzepatide dose?
It depends entirely on how you mixed the vial - the milligram dose alone does not set the units. You need the concentration. If a 10 mg vial is reconstituted with 2 mL of bacteriostatic water, the concentration is 5 mg/mL, so 2.5 mg is 0.5 mL, which is 50 units on a U-100 insulin syringe. Change the water volume and the unit count changes. Always compute from your own vial and mixing volume.
What does U-100 mean on an insulin syringe?
U-100 means the syringe is scaled for a fluid that contains 100 units per mL. On that scale the whole 1 mL mark is 100 units, 0.5 mL is 50 units, and 0.1 mL is 10 units. So units equal millilitres times 100. Most insulin syringes sold for at-home injection are U-100.
Is a milligram the same as a unit?
No, and treating them as the same is a common and dangerous mistake. A milligram is a mass of drug. A unit on an insulin syringe is a mark on a volume scale (one hundredth of a millilitre on a U-100 syringe). How many units hold a given milligram dose depends on the concentration of your solution, which you set when you add water to the vial.
How do I convert micrograms to milligrams?
Divide by 1000. There are 1000 micrograms (mcg) in 1 milligram (mg). So 250 mcg is 0.25 mg, and 500 mcg is 0.5 mg. Research peptide doses are often written in mcg while GLP-1 doses are usually written in mg, so it helps to convert everything to mg first, then work out the volume and units.
Sources
- [1]HUMULIN R (insulin human) injection - DailyMed label, Eli LillyConfirms the U-100 standard: insulin is supplied at 100 units/mL (U-100), so units equal millilitres times 100.
The conversions on this page are arithmetic. The only external fact is the U-100 syringe standard, cited above.
Keep reading
This page is educational information, not medical advice. GLP-1 medications are prescription drugs; dosing, escalation, and any combination with other compounds are decisions for you and a licensed prescriber, based on the actual product you hold and your own health. Figures here describe published FDA labels and clinical trials - they are not a recommendation to take any dose. Compounded and research-grade products can differ in concentration and purity from the approved versions these schedules were written for.