Retatrutide dose in units: mg-to-units conversion chart

A U-100 unit is a volume, not a dose. Converting milligrams of retatrutide to units therefore needs one more number: the concentration of the solution in mg/mL. This chart gives the conversion at five fixed concentrations and maps the trial dose steps onto them. Retatrutide is investigational and not approved by any regulator (Eli Lilly, Aug 12, 2026); for background see the retatrutide hub.

mg to units at five concentrations

Read across a row to see how the same mg amount reads at each concentration. “Over” means the reading exceeds the 100 units a 1 mL U-100 syringe holds; the number in brackets is what it would be.

Common vial and volume pairs produce these concentrations: 2.5 mg/mL is 5 mg in 2 mL or 10 mg in 4 mL; 3.333 mg/mL is 10 mg in 3 mL; 5 mg/mL is 10 mg in 2 mL; 10 mg/mL is 10 mg in 1 mL or 20 mg in 2 mL; 20 mg/mL is 20 mg in 1 mL or 60 mg in 3 mL. The units calculator handles any other combination.

The formula, step by step

Three lines cover every conversion:

1. Concentration: C (mg/mL) = vial mg ÷ water mL.
2. Volume: V (mL) = dose mg ÷ C.
3. Units: U = V × 100, because a U-100 scale has 100 units per mL.

Collapsed into one line: units = dose mg ÷ C × 100. The reverse, for reading a unit mark back to mg, is mg = units × C ÷ 100. Each unit therefore holds C ÷ 100 mg: 0.025 mg at 2.5 mg/mL, 0.0333 mg at 3.333 mg/mL, 0.05 mg at 5 mg/mL, 0.1 mg at 10 mg/mL and 0.2 mg at 20 mg/mL.

Trial dose steps in units

The Phase 3 TRIUMPH and TRANSCEND trials used five dose strengths, 2, 4, 6, 9 and 12 mg, starting at 2 mg and stepping up every 4 weeks (Eli Lilly, Dec 11, 2025). The Phase 2 obesity trial used an 8 mg step instead of 6 and 9 mg (Eli Lilly, hosted on ClinicalTrials.gov, Aug 29, 2022). The table maps each published step onto three concentrations.

Two patterns stand out. At 5 mg/mL, only the first two Phase 3 steps fit under 100 units. At 20 mg/mL, every step fits, but the 2 mg step reads only 10 units, where a half-unit rounding step is 5% of the reading. The week numbers come from the Phase 3 ladder in Lilly’s May 21, 2026 release (Eli Lilly, May 21, 2026); the titration calculator turns them into calendar dates.

Units back to mg

The same chart read in reverse shows what a unit mark corresponds to at each concentration.

This is why a unit number on its own says nothing about the amount. “20 units” is 1 mg at 5 mg/mL and 4 mg at 20 mg/mL, a fourfold difference.

Worked examples

Example 1. A 10 mg vial in 2 mL of water is 10 ÷ 2 = 5 mg/mL. For 2 mg: 2 ÷ 5 = 0.4 mL, and 0.4 × 100 = 40 units.

Example 2. A 20 mg vial in 2 mL is 10 mg/mL. For 9 mg: 9 ÷ 10 = 0.9 mL, which is 90 units, just under the 100-unit limit. For 12 mg: 1.2 mL, or 120 units, which exceeds a single 100-unit syringe.

Example 3. A 10 mg vial in 3 mL is 3.333 mg/mL. For 2 mg: 2 ÷ 3.333 = 0.6 mL, which is 60 units. For 4 mg: 1.2 mL, or 120 units, over the limit.

Example 4. A 30 mg vial in 2 mL is 15 mg/mL. For 4 mg: 4 ÷ 15 = 0.2667 mL, or 26.67 units, which rounds to 26.5 units. That rounded reading corresponds to 3.975 mg, 0.6% under 4 mg.

Rounding, readability and capacity

Our tools round every reading to the nearest 0.5 unit, because U-100 scales are marked in 1-unit or 2-unit steps. They flag readings under 2 units, where a half-unit step is 25% or more of the reading. They also check capacity: U-100 syringes come in 30-unit, 50-unit and 100-unit sizes, so a 60-unit reading fits only the 100-unit size. The reconstitution chart covers these limits, and dead space, in more detail, and the reconstitution calculator applies them to any vial.

What this chart does not cover

These are conversions, not doses. The trial steps above describe how Lilly’s trials were run and are reported as published facts. Retatrutide vials sold online carry labels no regulator has checked: the FDA has called retatrutide sold “for research purposes only” an unapproved new drug (FDA, Dec 10, 2024), including product sold under the street name “GLP-3R” (FDA, Aug 24, 2026). Any unit reading inherits the uncertainty of the labeled mg it starts from. The dosage chart has the full trial ladders and their results.