Molecular Weight Calculator (2026) – Chemical Molar Mass & Formula Weight

1. Molecular Weight & Molar Mass Equation

Where nᵢ is the integer subscript count of element i in the chemical formula and Aᵣ(i) is its standard IUPAC atomic weight in g/mol (or Daltons, Da).

2. Elemental Mass Percent Composition

Determines the exact percentage by mass that each element contributes to 1 mole of the compound—essential for elemental combustion analysis and purity verification.

3. Grams to Moles Conversion Formula

Converts weighed sample mass in grams (m) into chemical amount in moles (n). Multiplying moles by Avogadro's constant (6.02214076 × 10²³ mol⁻¹) yields total molecules.

4. Lab Solution Molarity Recipe Formula

Calculates the exact mass of solid reagent in grams required to prepare a target volumetric solution of desired molarity (M).

Water (H₂O) — 18.015 g/mol

• • Hydrogen (H): 2 × 1.008 = 2.016 g/mol
• • Oxygen (O): 1 × 15.999 = 15.999 g/mol
• Total MW = 2.016 + 15.999 = 18.015 g/mol

Mass Composition: 88.81% Oxygen, 11.19% Hydrogen.

Calcium Hydroxide (Ca(OH)₂) — 74.092 g/mol

• • Calcium (Ca): 1 × 40.078 = 40.078 g/mol
• • Oxygen (O): 2 × 15.999 = 31.998 g/mol
• • Hydrogen (H): 2 × 1.008 = 2.016 g/mol
• Total MW = 40.078 + 31.998 + 2.016 = 74.092 g/mol

The outer subscript 2 doubles both O and H inside (OH)₂.

Copper(II) Sulfate Pentahydrate (CuSO₄·5H₂O) — 249.685 g/mol

• • Cu (1 × 63.546) + S (1 × 32.06) = 95.606 g/mol
• • Oxygen (9 total: 4 + 5): 9 × 15.999 = 143.991 g/mol
• • Hydrogen (5 × 2 = 10): 10 × 1.008 = 10.080 g/mol
• Total MW = 249.677–249.685 g/mol

Includes 5 waters of crystallization (5 × 18.015 = 90.075 g/mol).

1. How do you calculate the molecular weight using a weight molecular calculator?

To calculate the molecular weight using our weight molecular calculator, enter any valid chemical formula (such as C6H12O6, H2SO4, or Ca(OH)2) into the input box. The parser automatically reads each element symbol, expands nested parentheses and hydrate coefficients, multiplies each atom count by its 2026 IUPAC standard atomic weight, and outputs the exact molar mass in g/mol alongside the monoisotopic mass in Da.

2. What is the difference between molecular weight (Da), molar mass (g/mol), and empirical formula weight?

Molecular weight is the mass of one single molecule expressed in unified atomic mass units (u or Daltons, Da). Molar mass is the mass in grams of one mole (6.02214076 × 10²³ molecules) of a substance, measured in g/mol. While numerically identical, they represent different scales. Empirical formula weight is the mass of the simplest whole-number ratio of atoms in the compound (for example, Glucose C₆H₁₂O₆ has a molecular weight of 180.156 g/mol, while its empirical formula CH₂O has an empirical weight of 30.026 g/mol).

3. How to calculate molecular weight when a formula contains parentheses or water of crystallization (hydrates)?

When a chemical formula contains parentheses—such as Al2(SO4)3—multiply the subscript of every element inside the parentheses by the subscript immediately outside the closing parenthesis (giving 2 Al, 3 S, and 12 O atoms). For hydrates containing water of crystallization—such as CuSO4·5H2O—calculate the molar mass of the anhydrous salt (CuSO4 = 159.602 g/mol) and add the mass of the water molecules multiplied by the leading hydrate number (5 × 18.015 = 90.075 g/mol) for a total of 249.677 g/mol.

4. Why does capitalization change a molecular weight calculation (e.g., Co vs. CO)?

In IUPAC chemical nomenclature, every element symbol starts with a capital letter, and any second letter is strictly lowercase. Entering Co represents a single atom of the transition metal Cobalt (58.933 g/mol), whereas entering CO in all-caps represents one atom of Carbon bonded to one atom of Oxygen—Carbon Monoxide (12.011 + 15.999 = 28.010 g/mol).

5. How do I calculate how many grams of chemical to weigh for a specific molarity (M) solution?

Use the laboratory molarity equation: Mass (g) = Concentration (mol/L) × Volume (L) × Molecular Weight (g/mol). For example, to prepare 500 mL (0.5 L) of a 0.5 M Glucose (180.156 g/mol) solution, multiply 0.5 mol/L × 0.5 L × 180.156 g/mol = 45.039 grams of solid glucose dissolved to 500 mL total volume.

6. What are the standard IUPAC atomic weights of the most common chemistry elements (H, C, N, O, Na, Cl, S)?

According to standard IUPAC atomic weights used in US AP Chemistry and university laboratories, the values in g/mol are: Hydrogen (H) = 1.008, Carbon (C) = 12.011, Nitrogen (N) = 14.007, Oxygen (O) = 15.999, Sodium (Na) = 22.990, Sulfur (S) = 32.060, and Chlorine (Cl) = 35.450.