Molecular Weight Conversion Calculator
Convert molecular weight between Daltons (Da), atomic mass units (amu), grams per mole (g/mol), and kiloDaltons (kDa). Enter a chemical formula to calculate the molecular weight, then use the value in any unit system. Understand the relationship between Da, amu, g/mol, and kDa — and when to use each in chemistry, biochemistry, and mass spectrometry.
Enter a chemical formula above to calculate molecular weight
Molecular Weight in All Units
Calculate once, express in any molecular weight unit.
Molecular weight units can be confusing because three common units — g/mol, Da, and amu — are all numerically identical. A water molecule has a molecular weight of 18.015 g/mol = 18.015 Da = 18.015 amu. The only conversion needed is to kDa: divide by 1000.
The choice of unit depends on your field: organic chemists use g/mol, biochemists use kDa for proteins, mass spectrometrists use Da and m/z ratios, and physicists use amu. This calculator gives results in g/mol, which can be used interchangeably with Da and amu.
For the absolute mass of a single molecule in grams, multiply the Da value by 1.66054 × 10⁻²⁴ g. But for all practical chemistry, the g/mol value is what you need.
Atomic Weights in Da / amu / g/mol
Each element's atomic weight can be expressed in any of these equivalent units.
Every atomic weight can be expressed in Da, amu, or g/mol — the values are identical. Carbon weighs 12.011 Da = 12.011 amu = 12.011 g/mol. The Dalton is named after John Dalton, who first proposed the atomic theory.
For biochemistry and proteomics, kiloDaltons (kDa) are practical: hemoglobin is ~64.5 kDa rather than 64,500 Da. Antibodies are typically ~150 kDa, and ribosomes reach ~2,500 kDa.
Explore element atomic weights below — each value works in Da, amu, and g/mol simultaneously.
How to Convert Molecular Weight Units
Calculate the molecular weight, then express it in any unit.
Enter a Chemical Formula
Type any formula from simple molecules to large biomolecules. The calculator computes the molecular weight in g/mol — the base unit from which all other molecular weight units can be derived. Results can be mentally converted: g/mol = Da = amu (all numerically equal).
Molecular Weight in Multiple Units
Click any compound to see its molecular weight expressed in all units.
Molecular Weight Conversion FAQ
Questions about Da, amu, g/mol, kDa, and unit conversions.