Converting tirzepatide mg to units takes three steps: concentration = tirzepatide in the vial / water added, draw volume = dose / concentration, and units on U-100 = draw volume x 100. For a 20 mg vial in 2 mL (10 mg per mL), a 5 mg dose is 0.5 mL, or 50 units. The arithmetic is the same as for any peptide; tirzepatide’s doses are simply larger, so a concentration error costs more on the barrel.
How do you convert tirzepatide mg to units?
concentration = tirzepatide in the vial / bacteriostatic water added
draw volume = dose in mg / concentration
units on U-100 = draw volume x 100Take a 20 mg vial reconstituted with 2 mL. That is 10 mg per mL.
- 2.5 mg is 0.25 mL, which is 25 units.
- 5 mg is 0.5 mL, which is 50 units.
- 7.5 mg is 0.75 mL, which is 75 units.
- 10 mg is 1 mL, which is 100 units, the whole barrel of a 1 mL syringe.
Notice what happens at the top of that list. Ten milligrams from a 10 mg per mL vial does not fit in a 0.5 mL barrel at all, and exactly fills a 1 mL one. The tirzepatide calculator warns when a draw is larger than the barrel you selected instead of returning a number you cannot measure.
Reconstitute the same 20 mg vial with 1 mL instead and it becomes 20 mg per mL, halving every draw above. Nothing about the vial changed except the water, which is the point made at length in how to reconstitute a peptide vial.
Doses per vial
Divide the vial by the dose. A 20 mg vial at 2.5 mg per dose is eight whole doses; at 7.5 mg per dose it is two whole doses with 5 mg left, which is not enough for a third. The calculator reports the whole doses and the remainder separately rather than printing 2.67, because two thirds of a dose is not a thing you can draw next week.
What the label says
The US labelling for the branded tirzepatide products starts at 2.5 mg once weekly for four weeks, then 5 mg once weekly, with further increases in 2.5 mg increments after at least four weeks at the current dose, to a maximum of 15 mg once weekly. The labelled elimination half life is about five days. Both figures are reproduced with their sources on the tirzepatide page, and reading a GLP-1 titration schedule covers how those steps are written.
A compounded vial is not the labelled product, and this site does not tell you which dose to use. It converts the dose you already have into a reading you can make.
In short: tirzepatide units = (dose / concentration) x 100 on a U-100 syringe, where concentration is the vial’s mg per mL after reconstitution.