Molecular Weight Calculator

Calculate molecular weight and molar mass from chemical formulas

Molecular Weight Calculator

Molecular Weight (MW): Sum of atomic masses of all atoms in a molecule.
Enter chemical formula (e.g., H2O, C6H12O6, Ca(OH)2)

Use capital letters for elements (H, C, O, etc.) and numbers for subscripts

Quick Examples:

Notes:

  • • Molecular weight = molar mass (g/mol)
  • • Based on standard atomic weights (C-12 scale)
  • • Use for converting between mass and moles
  • • Essential for stoichiometry calculations

Understanding Molecular Weight

Molecular weight (also called molar mass or formula weight) is the sum of the atomic masses of all atoms in a molecule. It's expressed in grams per mole (g/mol) and is essential for converting between mass and moles in chemistry calculations.

How to Calculate Molecular Weight

Example: Water (H₂O)

Step 1: Identify elements and their quantities

  • Hydrogen (H): 2 atoms
  • Oxygen (O): 1 atom

Step 2: Find atomic masses

  • H: 1.008 g/mol
  • O: 16.00 g/mol

Step 3: Calculate total mass

MW = (2 × 1.008) + (1 × 16.00)
MW = 2.016 + 16.00
MW = 18.016 g/mol

Common Molecular Weights

CompoundFormulaMW (g/mol)
WaterH₂O18.02
Carbon DioxideCO₂44.01
Sodium ChlorideNaCl58.44
GlucoseC₆H₁₂O₆180.16
Sulfuric AcidH₂SO₄98.08
CaffeineC₈H₁₀N₄O₂194.19

Using Molecular Weight in Calculations

Mass to Moles

moles = mass (g) / MW (g/mol)

Example: 36 g H₂O = 36 / 18.02 = 2.0 moles

Moles to Mass

mass (g) = moles × MW (g/mol)

Example: 0.5 mol CO₂ = 0.5 × 44.01 = 22 g

Applications

  • ⚖️
    Stoichiometry: Converting between mass and moles in chemical equations
  • 🧪
    Solution Preparation: Calculating mass needed for specific molar concentrations
  • 🔬
    Analytical Chemistry: Determining composition and purity of compounds
  • 💊
    Pharmaceuticals: Drug dosage calculations and formulation

⚖️Quick Reference

Units:

g/mol or amu/molecule

Formula:

Sum of atomic masses

1 mole:

6.022 × 10²³ molecules

🔗Related Calculators

📐Related Formulas

📊Mole vs Molar Mass

Understand the key differences between mole and molar mass

🎯Where It's Used

  • 🧪

    Lab Work

    Solution preparation

  • ⚖️

    Stoichiometry

    Mass-mole conversions