Lab calculator
Peptide stock solution concentration and molarity calculator (lab use)
Published 2026-10-29 · updated 2026-10-29 · vendor-authored explanatory note
Short answer
Molar concentration (mol/L) equals the amount of peptide in moles divided by the solution volume in liters. For a peptide: mM = 1000 × mass (mg) × net peptide content ÷ (molecular weight (g/mol) × volume (mL)). Correcting for net peptide content matters because lyophilized peptide powder also contains counter-ions and water. This calculator is for laboratory solution preparation only.
Stock solution calculator
For laboratory solution preparation only. Enter the measured quantity and net peptide content from the lot's certificate of analysis.
- Peptide concentration
- 5 mg/mL (5,000 µg/mL)
- Molar concentration
- 3.522 mM (3,522.4 µM)
- Solvent volume for the target concentration
- 3.522 mL
MW source: PubChem CID 9941957 (C62H98N16O22).
The formula
Amount of peptide (mmol) = mass of peptide (mg) ÷ molecular weight (g/mol). Concentration (mM) = amount (mmol) ÷ volume (L). Combining them: mM = 1000 × mg ÷ (MW × mL).
Worked example: 5 mg of a peptide with MW 1419.5 g/mol at 100% net content, in 1 mL, is 1000 × 5 ÷ (1419.5 × 1) = 3.52 mM, or about 3,522 µM.
To find the volume for a target concentration: volume (mL) = 1,000,000 × mg × net content ÷ (MW × target µM).
Correcting for net peptide content
Peptides purified by reverse-phase HPLC are commonly isolated as trifluoroacetate or acetate salts and retain some water. Net peptide content (often determined by amino-acid analysis or nitrogen analysis) is the fraction of the weighed mass that is the peptide itself. If a COA reports 80% net peptide content, 5 mg of powder contains 4 mg of peptide.
HPLC purity is different: it is the share of UV-absorbing material that is the target peptide, and it does not account for salts or water.
Good practice for stock solutions
Record the lot number, the COA values used, the solvent, the date, and the calculated concentration for every stock. Choose the solvent according to the peptide's solubility and the assay; buffer, pH and peptide sequence all affect solubility and stability.
Aliquot stocks to limit freeze-thaw cycles and store them as the assay protocol requires. See the storage guide linked below for general handling of lyophilized material.
Related on Vitality Chems
- Peptide molecular weight and CAS table — every molecular weight the calculator uses.
- Lyophilized peptide storage and handling — temperature, light and moisture.
- BPC-157 lot documentation — the worked example compound.
- Glossary: net peptide content — and other COA terms.
Frequently asked
How do I convert mg/mL to molarity for a peptide?
Divide the concentration in mg/mL by the molecular weight in g/mol and multiply by 1000 to get mM. For example 5 mg/mL of a 1419.5 g/mol peptide is 3.52 mM.
Should I use HPLC purity or net peptide content in the calculation?
Net peptide content, when the COA reports it, because it reflects how much of the weighed mass is peptide. HPLC purity describes the composition of the peptide material, not its salt and water content.
Where does the calculator's molecular weight come from?
From PubChem's computed average molecular weight for each listed compound (retrieved 2026-10-29). You can also enter a custom molecular weight.
Is this calculator for human or animal use?
No. It performs laboratory arithmetic for in-vitro solution preparation only. Research-use-only materials are not for human or animal use.
References
- PubChem (National Library of Medicine)Molecular weights used by the calculator.
- IUPAC Gold Book: amount concentrationDefinition of molar (amount) concentration.
