Calculator

Reconstitution calculator for any vial

Updated by the GLP Ladder Editorial Team. Editorial policy.

Short answer

Concentration = vial mg ÷ water mL; units = dose mg ÷ concentration × 100. Example: 10 mg + 2 mL = 5 mg/mL, so 2.5 mg = 50 units. For a target mark, water mL = vial mg × target units ÷ (dose mg × 100). Arithmetic as of Oct 19, 2026; not dosing advice.

Water mL = vial mg × target U ÷ (amount mg × 100)

Units on U-100
50 U (raw 50)
Volume
0.5 mL
Concentration
5 mg/mL
Draws per vial
4
Water for target mark
2 mL
Vial of 10 mg in 2 mL (5 mg/mL, 1 unit = 0.05 mg). Syringe drawn to 50 units of 100; nearest printed mark 50 units.123mL10 mg+ 2 mL water= 5 mg/mL4 draws00100.5201301.5402502.5603703.5804904.51005Umg3842465054586250
Vial of 10 mg in 2 mL (5 mg/mL, 1 unit = 0.05 mg). Syringe drawn to 50 units of 100; nearest printed mark 50 units.123mL10 mg+ 2 mL water= 5 mg/mL4 draws0010201304025060370804901005Umg3842465054586250

Lands exactly on a printed mark: 50 U.

1 unit = 0.05 mg · 10 units = 0.5 mg at 5 mg/mL.

Drag the plunger, or focus the diagram and use the arrow keys, to set the amount by syringe mark.

Water volumes that put 2.5 mg exactly on a printed mark of this syringe:

Syringe filled to 50 of 100 units 0102030405060708090100 50 U
U-100 scale: 100 units = 1 mL, so 1 unit = 0.01 mL. Units round to the nearest 0.5 U.

10 mg ÷ 2 mL = 5 mg/mL. 2.5 mg ÷ 5 mg/mL = 0.5 mL × 100 = 50 U.

Math, parameters and sources: model card.

From vial to syringe: the default example (10 mg vial, 2 mL water, 2.5 mg) in three steps

  1. Vial and water

    10 mg + 2 mL

    The mg in the vial never changes; water only sets how spread out it is.

  2. Concentration

    10 ÷ 2 = 5 mg/mL

    Milligrams in every milliliter of solution.

  3. Units on a U-100 syringe

    2.5 mg ÷ 5 = 0.5 mL = 50 U

    100 units = 1 mL, so units = mL × 100 (rounded to 0.5 U).

Vial × water chart

Pre-calculated U-100 readings for common vial sizes and water volumes. Every cell uses the same formula as the calculator. These are arithmetic tables for any lyophilized vial.

5 mg vial: U-100 units to draw for each dose (1 mL = 5 mg/mL; 2 mL = 2.5 mg/mL; 3 mL = 1.667 mg/mL)
Dose1 mL water5 mg/mL2 mL water2.5 mg/mL3 mL water1.667 mg/mL
0.25 mg 5 U10 U15 U
0.5 mg 10 U20 U30 U
1 mg 20 U40 U60 U
2 mg 40 U80 U—
2.5 mg 50 U100 U—
4 mg 80 U——
5 mg 100 U——
6 mg ———
8 mg ———
9 mg ———
10 mg ———
12 mg ———
10 mg vial: U-100 units to draw for each dose (1 mL = 10 mg/mL; 2 mL = 5 mg/mL; 3 mL = 3.333 mg/mL)
Dose1 mL water10 mg/mL2 mL water5 mg/mL3 mL water3.333 mg/mL
0.25 mg 2.5 U5 U7.5 U
0.5 mg 5 U10 U15 U
1 mg 10 U20 U30 U
2 mg 20 U40 U60 U
2.5 mg 25 U50 U75 U
4 mg 40 U80 U—
5 mg 50 U100 U—
6 mg 60 U——
8 mg 80 U——
9 mg 90 U——
10 mg 100 U——
12 mg ———
15 mg vial: U-100 units to draw for each dose (1 mL = 15 mg/mL; 2 mL = 7.5 mg/mL; 3 mL = 5 mg/mL)
Dose1 mL water15 mg/mL2 mL water7.5 mg/mL3 mL water5 mg/mL
0.25 mg 1.5 U (raw 1.67)3.5 U (raw 3.33)5 U
0.5 mg 3.5 U (raw 3.33)6.5 U (raw 6.67)10 U
1 mg 6.5 U (raw 6.67)13.5 U (raw 13.33)20 U
2 mg 13.5 U (raw 13.33)26.5 U (raw 26.67)40 U
2.5 mg 16.5 U (raw 16.67)33.5 U (raw 33.33)50 U
4 mg 26.5 U (raw 26.67)53.5 U (raw 53.33)80 U
5 mg 33.5 U (raw 33.33)66.5 U (raw 66.67)100 U
6 mg 40 U80 U—
8 mg 53.5 U (raw 53.33)——
9 mg 60 U——
10 mg 66.5 U (raw 66.67)——
12 mg 80 U——
20 mg vial: U-100 units to draw for each dose (1 mL = 20 mg/mL; 2 mL = 10 mg/mL; 3 mL = 6.667 mg/mL)
Dose1 mL water20 mg/mL2 mL water10 mg/mL3 mL water6.667 mg/mL
0.25 mg 1.5 U (raw 1.25)2.5 U4 U (raw 3.75)
0.5 mg 2.5 U5 U7.5 U
1 mg 5 U10 U15 U
2 mg 10 U20 U30 U
2.5 mg 12.5 U25 U37.5 U
4 mg 20 U40 U60 U
5 mg 25 U50 U75 U
6 mg 30 U60 U90 U
8 mg 40 U80 U—
9 mg 45 U90 U—
10 mg 50 U100 U—
12 mg 60 U——
30 mg vial: U-100 units to draw for each dose (1 mL = 30 mg/mL; 2 mL = 15 mg/mL; 3 mL = 10 mg/mL)
Dose1 mL water30 mg/mL2 mL water15 mg/mL3 mL water10 mg/mL
0.25 mg 1 U (raw 0.83)1.5 U (raw 1.67)2.5 U
0.5 mg 1.5 U (raw 1.67)3.5 U (raw 3.33)5 U
1 mg 3.5 U (raw 3.33)6.5 U (raw 6.67)10 U
2 mg 6.5 U (raw 6.67)13.5 U (raw 13.33)20 U
2.5 mg 8.5 U (raw 8.33)16.5 U (raw 16.67)25 U
4 mg 13.5 U (raw 13.33)26.5 U (raw 26.67)40 U
5 mg 16.5 U (raw 16.67)33.5 U (raw 33.33)50 U
6 mg 20 U40 U60 U
8 mg 26.5 U (raw 26.67)53.5 U (raw 53.33)80 U
9 mg 30 U60 U90 U
10 mg 33.5 U (raw 33.33)66.5 U (raw 66.67)100 U
12 mg 40 U80 U—
40 mg vial: U-100 units to draw for each dose (1 mL = 40 mg/mL; 2 mL = 20 mg/mL; 3 mL = 13.333 mg/mL)
Dose1 mL water40 mg/mL2 mL water20 mg/mL3 mL water13.333 mg/mL
0.25 mg 0.5 U (raw 0.63)1.5 U (raw 1.25)2 U (raw 1.88)
0.5 mg 1.5 U (raw 1.25)2.5 U4 U (raw 3.75)
1 mg 2.5 U5 U7.5 U
2 mg 5 U10 U15 U
2.5 mg 6.5 U (raw 6.25)12.5 U19 U (raw 18.75)
4 mg 10 U20 U30 U
5 mg 12.5 U25 U37.5 U
6 mg 15 U30 U45 U
8 mg 20 U40 U60 U
9 mg 22.5 U45 U67.5 U
10 mg 25 U50 U75 U
12 mg 30 U60 U90 U
60 mg vial: U-100 units to draw for each dose (1 mL = 60 mg/mL; 2 mL = 30 mg/mL; 3 mL = 20 mg/mL)
Dose1 mL water60 mg/mL2 mL water30 mg/mL3 mL water20 mg/mL
0.25 mg 0.5 U (raw 0.42)1 U (raw 0.83)1.5 U (raw 1.25)
0.5 mg 1 U (raw 0.83)1.5 U (raw 1.67)2.5 U
1 mg 1.5 U (raw 1.67)3.5 U (raw 3.33)5 U
2 mg 3.5 U (raw 3.33)6.5 U (raw 6.67)10 U
2.5 mg 4 U (raw 4.17)8.5 U (raw 8.33)12.5 U
4 mg 6.5 U (raw 6.67)13.5 U (raw 13.33)20 U
5 mg 8.5 U (raw 8.33)16.5 U (raw 16.67)25 U
6 mg 10 U20 U30 U
8 mg 13.5 U (raw 13.33)26.5 U (raw 26.67)40 U
9 mg 15 U30 U45 U
10 mg 16.5 U (raw 16.67)33.5 U (raw 33.33)50 U
12 mg 20 U40 U60 U

Units = dose mg ÷ (vial mg ÷ water mL) × 100, rounded to the nearest 0.5 U; the raw value is shown in brackets when rounding changed it. A dash means the draw would exceed a 100-unit syringe or the vial. Arithmetic only; not dosing advice.

Rounding, syringe size and dead space

Results round to the nearest 0.5 unit because U-100 syringes are marked in 1-unit (30 and 50 U) or 2-unit (100 U) steps; the raw value is always shown next to the rounded one. The calculator warns when a draw exceeds the chosen syringe or falls under 2 units, where a half-unit reading error is 25% or more of the amount. Dead space (liquid held in the hub and needle) does not change the units for one draw, but it lowers how many draws a vial yields.

Frequently asked questions

How much bacteriostatic water to reconstitute 10 mg retatrutide?

The water volume only sets the concentration; any volume works mathematically. 10 mg in 2 mL gives 5 mg/mL (2 mg = 40 units); in 1 mL it gives 10 mg/mL (2 mg = 20 units). Larger volumes give larger, easier-to-read unit counts. This is arithmetic, not a preparation instruction.

Are FDA-approved pens and vials reconstituted?

No. Zepbound, Mounjaro, Wegovy and Ozempic are supplied as ready-to-use solutions. Reconstitution math applies to lyophilized (freeze-dried) vials, which for these molecules are compounded or research products that the FDA has not approved.

How do I choose the water volume for a target unit mark?

Rearrange the formula: water mL = vial mg × target units ÷ (dose mg × 100). For a 10 mg vial and a 2.5 mg amount that should read 25 units, water = 10 × 25 ÷ 250 = 1 mL.

Does more water change the amount of drug?

No. The vial mg is fixed; water only spreads it over more volume. Doubling the water halves the concentration and doubles the units needed for the same mg.

Is this calculator specific to one compound?

No. The math is the same for any lyophilized vial: it needs only the mg in the vial, the mL of diluent and the target amount. Compound-specific versions add the published dose steps for retatrutide, tirzepatide and semaglutide.

Sources

  1. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. U.S. Food and Drug Administration, Oct 1, 2026. Accessed Oct 19, 2026.
  2. FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize. U.S. Food and Drug Administration, Apr 1, 2026. Accessed Oct 19, 2026.

Printed from GLP Ladder. To recreate this result, open https://glpladder.com/tools/reconstitution/

Questions for my clinician

Tools

Guides and data