Why units instead of milligrams
Reconstituted tirzepatide is drawn up with an insulin syringe marked in units, not millilitres or milligrams. A dosing chart in units exists to bridge that gap: it tells you how many units on the syringe correspond to a given mg dose, based on how much bacteriostatic water was used to reconstitute the vial.
The maths behind the chart
The concentration after reconstitution depends entirely on how much liquid was added to the powder. A 10mg vial mixed with 2mL of bacteriostatic water gives 5mg per mL, or 0.5mg per 10 units on a standard 100-unit insulin syringe. Change the water volume and every number on the chart changes with it, which is why a chart is only correct for the specific reconstitution ratio it was built for.
Reading the chart correctly
A properly labelled chart states the vial size, the water volume used, and the resulting concentration before listing dose-to-unit conversions. If a chart is missing any of those three numbers, the unit values on it can’t be trusted, even if the final numbers look reasonable.
A worked example
For a 10mg vial mixed with 2mL of water (5mg/mL): 2.5mg is 50 units, 5mg is 100 units, 7.5mg is 150 units (needing two draws on a 100-unit syringe). These numbers only hold for that exact 2mL mix; a 1mL mix would double the concentration and halve every unit figure.
Before trusting any chart
Cross-check a chart against the vial’s own label and the actual water volume used, not just the mg total. A chart copied from a different reconstitution ratio is the most common source of dosing errors reported in community discussions.