Molecular Weight Calculator

Calculate molecular weights and molar masses for any chemical compound. Supports complex formulas, hydrates, and isotopic compositions.

Molecular Weight Formula: M = Σ(nᵢ × Aᵢ)

Where: nᵢ = number of atoms of element i, Aᵢ = atomic weight of element i

Choose from 50+ common compounds or enter your own formula below
Enter a chemical formula. Use standard notation: H2O, C6H12O6, CH3COOH, Na2SO4·10H2O, etc.
Complex Formula Examples:
Ammonium Sulfate
Gypsum
Catalyst
Ferrocyanide
Polyethylene
Water
Glucose
Sodium Chloride
Carbon Dioxide
Sulfuric Acid
Acetic Acid
Sucrose
Sodium Carbonate
Calcium Carbonate
Caffeine
Click on elements to add them to your formula. Colors indicate element groups.

Understanding Molecular Weight

Molecular weight (also called molecular mass or molar mass) is the sum of the atomic weights of all atoms in a molecule. It's expressed in atomic mass units (u) or grams per mole (g/mol).

Key Formula:

Molecular Weight (M) = Σ(nᵢ × Aᵢ)

Where: nᵢ = number of atoms of element i, Aᵢ = atomic weight of element i

Hydrate Notation: Use · or . to separate water molecules (e.g., CaSO4·2H2O). The calculator will correctly parse and calculate the total molecular weight including hydrate water.

How to Write Chemical Formulas

Notation Example Explanation
Element symbols H, O, C, Na, Cl Use standard element symbols (first letter uppercase, second lowercase)
Subscripts H2O, CO2 Number of atoms follows the element symbol (no space)
Parentheses (NH4)2SO4 Groups in parentheses with subscript apply to entire group
Nested Parentheses ((C6H5)3P)2PdCl2 Supports multiple levels of nested parentheses
Hydrates CuSO4·5H2O Use middle dot (·) or period to separate hydrate water
Charges SO42-, NH4+ Ionic charges are superscripts after the formula
Isotopes 13C, D2O Isotopic mass numbers are superscripts before the element

Common Elements and Atomic Weights

Element Symbol Atomic Number Atomic Weight (u)

Importance of Molecular Weight

1

Stoichiometry: Essential for balancing chemical equations and calculating reactant/product quantities.

2

Solution Preparation: Needed to prepare solutions of specific molarity (mol/L).

3

Analytical Chemistry: Used in mass spectrometry, chromatography, and other analytical techniques.

4

Pharmaceuticals: Critical for drug dosage calculations and formulation development.

5

Material Science: Important for polymer characterization and material properties.

Applications of Molecular Weight

  • Chemistry Labs: Preparing solutions with precise concentrations
  • Biochemistry: Determining protein and DNA molecular weights
  • Pharmacy: Calculating drug dosages and formulations
  • Environmental Science: Analyzing pollutants and their concentrations
  • Industrial Chemistry: Process design and quality control

Calculator Features:

  • Supports complex formulas with parentheses, hydrates, and isotopic notation
  • Uses IUPAC standard atomic weights (2019 values)
  • Provides detailed elemental breakdown with percentages
  • Visualizes composition with interactive pie chart
  • Includes periodic table for easy element selection
  • Contains database of 50+ common compounds

Frequently Asked Questions

Molecular weight is the mass of a single molecule in atomic mass units (u), while molar mass is the mass of one mole of substance in grams per mole (g/mol). Numerically, they are equal (1 u = 1 g/mol), but they have different units and contexts.

The calculator uses standard atomic weights which represent the weighted average of naturally occurring isotopes. For specific isotopic formulas (like 13C or D2O), it uses the exact isotopic masses when specified in the formula.

Yes, the calculator works for both molecular and ionic compounds. For ionic compounds like NaCl, it calculates the formula weight (sum of atomic weights of all ions in the formula unit).

The calculator uses IUPAC standard atomic weights (2019 values), which are based on the most recent measurements and isotopic abundance data. For most educational and many professional purposes, these values are sufficiently accurate.

The calculator supports formulas with multiple levels of parentheses, hydrates, and isotopic notation. However, extremely complex formulas with nested parentheses more than 3 levels deep may not parse correctly. For such cases, use the formula builder tool.