Molecular Weight Calculator

Calculate molecular weight (molar mass) from chemical formula

Enter Chemical Formula

Examples: H2O, CO2, NaCl, C6H12O6

Molecular Weight Result

Formula:H2O
Molecular Weight:18.02 g/mol

Element Breakdown:

H (2 atoms):1.01 × 2 = 2.02 g/mol
O (1 atom):16.00 × 1 = 16.00 g/mol

About This Calculator

The Molecular Weight Calculator helps you calculate the molecular weight (molar mass) of a chemical compound from its formula. Molecular weight is the sum of the atomic weights of all atoms in a molecule, expressed in grams per mole (g/mol).

This tool is essential for chemistry students, researchers, and professionals who need to determine molecular weights for stoichiometry calculations, solution preparation, and chemical analysis. Enter the chemical formula using standard notation (e.g., H2O, CO2, NaCl).

Formula & Calculation Method

Molecular weight is calculated using the formula:

MW = Σ(Atomic Weight × Number of Atoms)

Where:

  • MW = Molecular Weight (g/mol)
  • Atomic Weight = Atomic mass of each element
  • Number of Atoms = Count of each element in the molecule

Example: For H2O (water):

  • 2 × H (1.008 g/mol) = 2.016 g/mol
  • 1 × O (15.999 g/mol) = 15.999 g/mol
  • Total = 18.015 g/mol

How to Use This Calculator

Frequently Asked Questions

What is molecular weight?

Molecular weight (also called molar mass) is the sum of the atomic weights of all atoms in a molecule, expressed in grams per mole (g/mol). It represents the mass of one mole of the compound.

How is molecular weight different from atomic weight?

Atomic weight is the average mass of an atom of an element, while molecular weight is the sum of atomic weights for all atoms in a molecule. For example, H has atomic weight 1.008 g/mol, while H2O has molecular weight 18.015 g/mol.

What units are used for molecular weight?

Molecular weight is typically expressed in grams per mole (g/mol) or atomic mass units (amu). In chemistry, g/mol is the standard unit used in calculations.

Can I calculate molecular weight for complex compounds?

Yes, as long as you enter the correct chemical formula. The calculator sums the atomic weights of all elements in the formula. For very complex molecules, ensure you have the correct molecular formula.

Calculator by

NumCalculators Editorial Team

Multi-disciplinary Expert Team

Updated Jan 2024