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Concentration calculator

For preparing laboratory stock and working solutions. Stock concentration (mg/mL) = mass ÷ volume; molarity (µM) = (mg/mL ÷ molecular weight in g/mol) × 10⁶.

5 mg/mL · stock concentration 3,522.4 µM (3.522 mM)

Dilute stock 1 : 35.2: e.g. 28.39 µL stock per 1 mL final volume.

Worked example

A vial holds 5 mg of lyophilised peptide with a molecular weight of 1,000 g/mol, made up in 2.0 mL of diluent.

  1. Stock concentration: 5 mg ÷ 2.0 mL = 2.5 mg/mL.
  2. Molarity: 2.5 mg/mL is 2.5 g/L; 2.5 ÷ 1,000 g/mol = 0.0025 mol/L, which is 2,500 µM (2.5 mM).
  3. Working solution: for 1 mL at 10 µM, C₁V₁ = C₂V₂ gives V₁ = (10 µM × 1 mL) ÷ 2,500 µM = 0.004 mL, so 4 µL of stock made up to 1 mL (a 1:250 dilution).

Use the molecular weight on the certificate or specification for the exact lot. A salt form (for example TFA or acetate) changes the mass per mole, and the HPLC purity figure is not the same as net peptide content. See net peptide content vs purity.