Preparation
Concentration math
mg, mcg, mL, units — the four conversions and one equation behind every reconstitution question, with worked examples you can check by hand.
One equation, everything else is conversion
Every reconstitution calculation on earth is the same arithmetic:
concentration = peptide amount ÷ liquid volume
Dissolve 5 mg in 2 mL and the concentration is 2.5 mg/mL. Dissolve the same 5 mg in 5 mL and it is 1 mg/mL. Nothing about the peptide changes; only how tightly packed the molecules are in the liquid changes. Every other number people ask about — “how much per unit”, “what volume for X mcg” — is this equation rearranged.
The four conversions
| Conversion | Rule |
|---|---|
| mg → mcg | 1 mg = 1,000 mcg (multiply by 1,000) |
| mcg → mg | 1,000 mcg = 1 mg (divide by 1,000) |
| mL → units (U100 syringe) | 1 mL = 100 units; 10 units = 0.1 mL |
| concentration per unit | mg per mL ÷ 100 = mg per unit |
Worked example calculation
These numbers are a demonstration of the arithmetic, not a preparation recommendation — the vial amounts and diluent volumes are chosen to make the math legible.
| Step | Values | Result |
|---|---|---|
| Vial amount | 10 mg peptide | — |
| Diluent added | 2 mL | — |
| Concentration | 10 mg ÷ 2 mL | 5 mg/mL |
| Per 10 units (0.1 mL) | 5 mg/mL × 0.1 mL | 0.5 mg = 500 mcg |
| Volume for a target 250 mcg | 250 mcg ÷ 5,000 mcg/mL | 0.05 mL = 5 units |
Changing an input changes everything
Change any input and every downstream number changes: the same 10 mg in 5 mL halves the concentration to 2 mg/mL, and that same 250 mcg target becomes 12.5 units. This is why no calculator can tell you “the” answer — there isn't one until someone chooses the inputs.
Where people go wrong
- —Reading a syringe's units as milligrams. Units mark volume (0.01 mL each), never mass.
- —Forgetting net peptide content. A “5 mg” vial whose certificate says 85% net content holds 4.25 mg of peptide; concentration math on the label number overstates the solution by that gap.
- —Adding diluent volume to a dissolved cake's volume. The reconstituted volume is slightly more than the diluent alone; precise work uses final volume, not diluent volume.
- —Halving concentration by halving diluent — correct — but then re-stating the old per-unit number. Recompute the whole chain every time an input changes.
Do it yourself
The reconstitution calculator performs exactly these steps on values you enter, shows the equation it used, and produces a shareable URL that encodes the calculation. A printable reference table for common vial sizes and diluent volumes is available there too.
Updated 17 September 2026 · Therapept Editorial · How these guides are built