Peptide concentration math comes down to two steps: find the concentration (mass of peptide divided by the volume of solvent you added), then find the volume of that stock needed for a working solution (the peptide mass the working solution requires divided by that concentration). This article walks through it in plain language, with a worked example.
Step 1: the units
Weight is measured in milligrams (mg) and micrograms (mcg): 1,000 micrograms (mcg) = 1 milligram (mg), so 100 mcg = 0.1 mg. To convert mcg to mg, divide by 1,000. Volume is measured in milliliters (mL) and microliters (µL): 1 milliliter (mL) = 1,000 microliters (µL).
Step 2: the two-step calculation
First, concentration: concentration (mg/mL) = peptide in the vial (mg) ÷ solution added (mL). Second, volume of stock: volume of stock (mL) = peptide mass the working solution requires (mg) ÷ stock concentration (mg/mL). Convert any mcg amount to mg first so both numbers share a unit.
A worked example
Suppose a vial holds 5 mg of peptide and you add 2 mL of solvent. Stock concentration = 5 mg ÷ 2 mL = 2.5 mg/mL. To prepare 1 mL of a 0.25 mg/mL working solution for an in vitro assay, the working solution requires 0.25 mg/mL × 1 mL = 0.25 mg of peptide. Volume of stock = 0.25 mg ÷ 2.5 mg/mL = 0.1 mL (100 µL), brought to 1 mL with assay buffer.
Use the calculator
Our interactive reconstitution calculator does this math for you and shows the result in milliliters: see the reconstitution calculator.
Related research guides
- mg/mL and molarity explained
- Stock & working solutions (serial dilution)
- mcg, mg & molarity units primer
- Molar concentration: worked example
- How to reconstitute lyophilized peptides
Research-use note
This describes laboratory concentration math for in vitro research use only. It is not a dose or an instruction for use in a person or animal.
Related research: LIPO-C | MIC-C.
