Molecular Weight Calculator

Calculate molecular weight from chemical formula. Parses element symbols and subscripts.

Molecular Weight

18.015 g/mol

Element Breakdown

H × 22.016 g/mol
O × 115.999 g/mol

Use the Molecular Weight Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Our Molecular Weight Calculator accurately determines the molecular weight of a compound from its chemical formula. This is crucial for various scientific and industrial applications, from precise reagent preparation in research labs to optimizing chemical processes in manufacturing, where even small deviations can significantly impact outcomes and costs. For instance, in pharmaceutical development, accurate molecular weights are essential for drug dosage calculations, ensuring patient safety and efficacy, a field projected to be worth over $1.7 trillion by 2026.

The calculator parses the chemical formula, identifying each element symbol and its corresponding subscript. It then references a comprehensive database of atomic weights for each element, using the latest IUPAC values. The molecular weight is calculated by summing the products of each element's atomic weight and its count within the molecule.

Ensure correct capitalization for element symbols (e.g., 'Co' for Cobalt, not 'CO' for Carbon Monoxide). Be mindful of parentheses; for example, 'Mg(OH)2' means two hydroxyl groups. A common mistake is forgetting to include the implied '1' subscript when an element appears without an explicit number, such as in 'H2O' where Oxygen has a subscript of 1.

Example: Calculating the Molecular Weight of Glucose

  1. 1 Input the chemical formula for glucose: C6H12O6.
  2. 2 The calculator identifies Carbon (C) with a subscript of 6, Hydrogen (H) with a subscript of 12, and Oxygen (O) with a subscript of 6. Using current atomic weights (C ≈ 12.011 g/mol, H ≈ 1.008 g/mol, O ≈ 15.999 g/mol), it calculates: (6 * 12.011) + (12 * 1.008) + (6 * 15.999).
  3. 3 The calculated molecular weight is approximately 180.156 g/mol.
  4. 4 This molecular weight is vital for biochemists determining concentrations in metabolic studies or for food scientists analyzing carbohydrate content, especially as global demand for food analysis and quality control is expected to reach $29 billion by 2026.

Source: Khan Academy · Last updated: April 2026

Frequently Asked Questions

How do you calculate molecular weight from a formula?
Add the atomic weights of all atoms in the formula. For H₂O: (2 x 1.008) + (1 x 16.00) = 18.016 g/mol. For glucose C₆H₁₂O₆: (6 x 12.01) + (12 x 1.008) + (6 x 16.00) = 180.16 g/mol.
What is the difference between molecular weight and molar mass?
They are numerically identical but have different units. Molecular weight is measured in atomic mass units (amu) for a single molecule. Molar mass is in grams per mole (g/mol) for Avogadro's number of molecules.
Where do you find atomic weights for calculation?
Atomic weights are listed on the periodic table under each element symbol. Common values include H = 1.008, C = 12.011, N = 14.007, O = 15.999, and S = 32.065.

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