Da · amu · kDa · g/mol

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.

= amu = g/mol

kDa

= 1000 Da

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Masse Molaire

Les 118 éléments · Poids atomiques IUPAC 2021

Exemples rapides:

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Entrez une formule ci-dessus pour calculer la masse molaire

Unit Conversion

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.

Formula Input

Atomic Weights

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.

Hydrogen

1.0080

Carbon

12.0110

Nitrogen

14.0070

Oxygen

15.9994

Sulfur

32.0650

Phosphorus

30.9738

Iron

55.8450

Cobalt

58.9332

Copper

63.5460

Zinc

65.3800

Molybdenum

95.9500

Gold

196.9665

How to Use

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).

C₈H₁₀N₄O₂

↓

194.19 g/mol

Examples

Molecular Weight in Multiple Units

Click any compound to see its molecular weight expressed in all units.

FAQ

Molecular Weight Conversion FAQ

Questions about Da, amu, g/mol, kDa, and unit conversions.

What units is molecular weight measured in?

Molecular weight can be expressed in several numerically equivalent units: grams per mole (g/mol), Daltons (Da), and atomic mass units (amu).

What is a Dalton (Da)?

A Dalton (Da) is a unit of mass equal to 1/12 the mass of a carbon-12 atom, or approximately 1.66054 × 10⁻²⁴ grams.

What is the difference between Da, amu, and g/mol?

Da (Dalton) and amu (atomic mass unit) are identical: both equal 1/12 the mass of carbon-12.

What is a kiloDalton (kDa)?

A kiloDalton (kDa) equals 1000 Daltons.

How do I convert between molecular weight units?

The conversions are simple: g/mol ↔ Da ↔ amu are all numerically equal (1:1:1).

What is m/z in mass spectrometry?

m/z (mass-to-charge ratio) is the quantity measured by a mass spectrometer.

Why do different sources report slightly different molecular weights?

Differences arise from: (1) Different IUPAC revision years for atomic weights, (2) Rounding to different decimal places, (3) Using monoisotopic mass vs average mass — monoisotopic uses the most abundant isotope of each element, while average uses the natural isotope distribution.