For research and educational purposes only. Not medical advice.
GLP-1 dose-to-units conversion formula
Convert a GLP-1 dose in mg to insulin-syringe units: draw in ml is dose over vial concentration, then times 100. Worked semaglutide and tirzepatide examples.
Branded GLP-1 pens hide this math behind a click dial. A reconstituted research vial does not, so you have to convert a dose in milligrams into a volume you can measure on an insulin syringe. This is the conversion that trips people up, and getting a decimal place wrong is exactly the error that shows up in poison-control and FDA dosing-error reports.
The conversion is two short steps of arithmetic, and it works in both directions. This page shows the formula, several worked examples for semaglutide- and tirzepatide-typical vials, and the mistakes worth being paranoid about.
Formulas and worked examples
Milligrams to syringe units
draw = dose (mg) / C ; units = draw (ml) x 100
draw (ml) = dose in mg / vial concentration in mg/ml; U-100 units = draw in ml x 100
- dose: the target dose, in milligrams (mg). For weekly GLP-1s this is the weekly dose.
- C: the reconstituted vial concentration, in milligrams per milliliter (mg/ml)
- draw: the volume to pull into the syringe, in milliliters (ml)
- units: the reading on a U-100 insulin syringe. 1 unit is 0.01 ml.
Worked examples
A 0.25 mg starter dose from a 2.5 mg/ml vial.
- 0.25 mg / 2.5 mg/ml = 0.1 ml.
- 0.1 ml x 100 = 10 units.
= 0.1 ml, which reads as 10 units
A 5 mg tirzepatide-typical dose from a 10 mg/ml vial.
- 5 mg / 10 mg/ml = 0.5 ml.
- 0.5 ml x 100 = 50 units.
= 0.5 ml, which reads as 50 units
A 2.4 mg semaglutide-typical dose from a 5 mg/ml vial.
- 2.4 mg / 5 mg/ml = 0.48 ml.
- 0.48 ml x 100 = 48 units.
= 0.48 ml, which reads as 48 units
- A result below 1 unit (for example, a very low dose from a very concentrated vial) is hard to measure on a 100-unit barrel.
- A result above 100 units does not fit in one 1 ml U-100 syringe.
Syringe units back to milligrams
dose = (units / 100) x C
dose (mg) = (U-100 units / 100) x vial concentration in mg/ml
- units: the number of U-100 units drawn
- C: the vial concentration, in mg/ml
- dose: the dose that draw delivers, in milligrams (mg)
Worked examples
You drew 40 units from a 5 mg/ml vial. What dose is that?
- 40 units / 100 = 0.4 ml.
- 0.4 ml x 5 mg/ml = 2 mg.
= 2 mg
- This is the exact inverse of the milligrams-to-units step, so a round trip must return the number you started with.
Common mistakes
- Reading "units" as milliliters. 50 units is 0.5 ml, not 50 ml.
- Using a U-40 syringe with U-100 math. On a U-40 barrel the same mark is a different volume, so the unit count is wrong.
- Applying pen-click logic to a vial. A pen doses in fixed clicks; a vial dose depends on the concentration you reconstituted to.
- A slipped decimal on the vial concentration or the dose. A 10x error here is the classic overdose pattern behind published GLP-1 dosing-error alerts.
- Assuming every vendor vial is the same concentration. It depends on how much bacteriostatic water was added, so confirm the concentration before converting.
Frequently asked questions
- How do I convert a GLP-1 dose in mg to units?
- Divide the dose in milligrams by the vial concentration in mg/ml to get the draw in milliliters, then multiply by 100 for U-100 insulin-syringe units. A 0.25 mg dose from a 2.5 mg/ml vial is 0.1 ml, which is 10 units.
- How many units is 5 mg of tirzepatide?
- It depends entirely on the vial concentration. From a 10 mg/ml vial, 5 mg is 0.5 ml, which is 50 units on a U-100 syringe. From a 5 mg/ml vial, the same 5 mg is 1 ml, which is 100 units. Always convert against your own vial concentration.
- How do I go from units back to a dose in mg?
- Divide the units by 100 to get milliliters, then multiply by the vial concentration in mg/ml. 40 units from a 5 mg/ml vial is 0.4 ml, which is 2 mg.
- Is this the same as how a Wegovy or Mounjaro pen doses?
- No. FDA-approved pens are pre-mixed at fixed concentrations and dose through a click mechanism with their own instructions. This formula is for a reconstituted research vial drawn with an insulin syringe, where the concentration is whatever you reconstituted to.
For research and educational purposes only. Not medical advice.