Reconstitution Calculator
How much diluent to add to a vial of powder to reach a target concentration, and the volume that then contains a required amount — for lab reagents, peptides and lyophilised standards.
Concentration is mass over volume, so the diluent to add is the powder mass divided by the concentration you want (a small correction for the powder’s own volume is usually ignored).
How the reconstitution calculator works
Concentration is mass over volume, so the diluent to add is the powder mass divided by the concentration you want (a small correction for the powder’s own volume is usually ignored). Once reconstituted, the volume holding a given amount is that amount divided by the concentration. Keep the units consistent: milligrams and millilitres give mg/mL; micrograms and microlitres give µg/µL, which is the same number.
Formula: volume to add = mass ÷ target concentration; dose volume = amount needed ÷ concentration
Worked examples
| Inputs | Diluent to add | Note |
|---|---|---|
| 5 mg to 1 mg/mL, 0.25 mg per use | 5 mL | add 5 mL; 250 µL per use, 20 uses |
| 1 mg to 2 mg/mL | 0.5 mL | add 0.5 mL; 50 µL per use |
| 100 mg to 25 mg/mL | 4 mL | add 4 mL |
FAQFrequently asked questions
Does the powder add volume?
A little — a few microlitres per milligram for most solids. For a 5 mg vial made up to 5 mL the error is under 1%; for very concentrated stocks, make up to a final volume in a volumetric flask instead of adding a fixed diluent.
What diluent should I use?
Whatever the datasheet says: sterile water, saline, buffer or DMSO for poorly soluble compounds. Some peptides need a drop of acid or base to dissolve; add it before making up the volume.
How do I get a molar concentration?
Divide the mg/mL figure by the molar mass in g/mol and multiply by 1,000 for mM. A 1 mg/mL solution of a 500 g/mol compound is 2 mM.
How long does a reconstituted vial keep?
It depends on the substance — hours for some enzymes, weeks frozen in aliquots for many peptides. Aliquot to avoid freeze–thaw cycles and follow the supplier’s stability note.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.