Reference tool
Molarity calculator
Convert between mass, volume and molar concentration. Pick a compound to load its molar mass, or type your own for anything not in the catalogue.
Calculator
How the arithmetic works
moles = mass (g) ÷ molar mass (g/mol)
molarity (M) = moles ÷ volume (litres)
In the units peptide work actually uses, milligrams and millilitres, those two steps collapse into one: millimolar concentration equals the mass in milligrams divided by the molar mass, divided by the volume in millilitres, times one thousand.
Mass concentration and molar concentration are not interchangeable. Two compounds at the same mg/ml hold different numbers of molecules whenever their molar masses differ, which is why any comparison across compounds has to be made in molar terms.
Questions
How do you calculate the molarity of a peptide solution?
Molarity is moles per litre. Divide the mass in grams by the molar mass in grams per mole to get moles, then divide by the volume in litres. For peptide work the practical form is: molarity (mM) = (mass in mg ÷ molar mass in g/mol) ÷ volume in ml × 1000.
What is the molar mass of a peptide?
It is the sum of the residue masses of every amino acid in the sequence, plus the mass of one water molecule for the free termini. It is usually quoted in grams per mole, and for the compounds in this catalogue it is listed on each product page where known.
Why use molarity instead of mg/ml?
Mass concentration says nothing about the number of molecules present. Two peptides at the same mg/ml differ in molar concentration by the ratio of their molar masses, so any work comparing receptor occupancy or binding across different compounds has to be done in molar terms.
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