Free tool
Peptide molar conversion
Where a protocol is specified in molar rather than mass terms, molecular weight is the bridge. Enter a molecular weight and a mass, or a concentration, and the conversions follow.
The molecular weight, and your numbers
Pick a compound below to fill the molecular weight, or type one in.
Your answer
Mass to moles, and concentration to molarity.
Show the other figures
- Same in nanomoles
- — nmol
- Molarity at that concentration
- — mM
- Same in micromolar
- — µM
- Mass of one micromole
- — mg
Arithmetic only. This tool converts between mass, volume and concentration for laboratory preparation and dilution planning. It is not dosing guidance, and nothing here is a therapeutic claim. All materials are supplied for in-vitro laboratory research use only.
How the arithmetic works
moles = mass ÷ molecular weight
Molecular weight varies enormously across this catalog — from around 160 g/mol for the smallest materials to over 5,000 for the long-chain analogues. That means a given mass contains wildly different molar quantities depending on the compound, which is exactly why mass-based comparisons between compounds mislead.
Two cautions. Use the average molecular weight for weighing and molar arithmetic; the monoisotopic mass is for comparing against a mass-spectrometry result and is a different number. And these conversions assume pure peptide — if you are working from label mass rather than peptide mass, correct for peptide content first.
Frequently asked
How do I convert peptide mass to moles?
Divide mass by molecular weight. Milligrams divided by g/mol gives millimoles; multiply by 1000 for micromoles. A 10 mg vial of a 1419.5 g/mol peptide contains about 7.045 µmol.
Should I use average or monoisotopic molecular weight?
Average, for anything involving weighing or molar concentration. Monoisotopic mass is the figure a mass-spectrometry result is compared against and diverges from the average as molecules get larger.
Where do I find a molecular weight?
Every compound page on this site lists it alongside the molecular formula and PubChem CID, sourced from PubChem. It is also stated on most certificates of analysis.
Related guides, definitions and calculators
Vial sizes and prices per milligram for every single vial and every 10-vial kit in the catalog are listed on one page each.