Peptide Concentration Calculator: mg, mL and Laboratory Aliquots

Use this guide to check mass-and-volume arithmetic in a laboratory preparation record. The examples are hypothetical; they do not specify a procedure for a particular compound.

The two formulas

Concentration (mg/mL) = nominal mass (mg) ÷ final solution volume (mL).

Aliquot mass (µg) = concentration (mg/mL) × aliquot volume (µL). The second expression works because the conversion from millilitres to microlitres cancels the conversion from milligrams to micrograms.

Use the laboratory calculator

Enter the mass basis and final volume from your method. The calculator rejects zero, negative or non-finite values and an aliquot larger than the prepared solution. It does not select a solvent or calculate an administration schedule.

A worked example with units

A hypothetical sample contains a nominal 10 mg of material and is made to a final volume of 2 mL. Its nominal concentration is 10 ÷ 2 = 5 mg/mL. A 100 µL aliquot equals 0.1 mL, so it contains 5 × 0.1 = 0.5 mg, or 500 µg.

What the calculator assumes

• The entered mass has the reporting basis your method requires.
• The material is dissolved and the solution is sufficiently homogeneous for sampling.
• The final volume and aliquot volume are measured appropriately.
• No correction for recovery, adsorption, measurement uncertainty or independently measured content is included.

Do not multiply nominal mass by an HPLC area percentage and assume that this establishes measured peptide content. Read purity, identity and quantity before applying an analytical correction.

Common errors to check

Confusing mg with µg creates a thousand-fold error. Confusing mL with µL does the same. Keep units in each step, use the final solution volume, and check the result independently against your laboratory method. Rounded display values should not be treated as a measurement-precision claim.

For solvent and preparation records, continue to the reconstitution guide.