How do I calculate molecular weight?

Sum up the atomic weights of all atoms in the molecular formula. For H₂O: 2(1.008) + 15.999 = 18.015 g/mol.

A Dalton (Da) is a unit of mass equal to 1/12 the mass of a carbon-12 atom. It's commonly used in biochemistry for protein sizes.

How do I handle parentheses in formulas?

Multiply the subscript outside the parentheses by each atom inside. Ca(OH)₂ has 1 Ca, 2 O, and 2 H atoms.

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Molecular Weight Calculator

Q: Is molecular weight the same as molar mass?

They are numerically identical when expressed in g/mol. Molecular weight is technically dimensionless, while molar mass has units.

Common Compounds

Water (H2O)

Chemical Formula

Use standard notation: H2O, Ca(OH)2, C6H12O6

Molecular Weight Calculator: Compute Molar Mass from Any Formula

Our Molecular Weight Calculator instantly computes the molecular weight (molar mass) of any chemical compound from its molecular formula. Simply enter a formula like H₂O, NaCl, or C₆H₁₂O₆ and get the precise molecular weight in g/mol.

Knowing the molecular weight of a compound is essential for stoichiometry, solution preparation, spectroscopy, and countless other applications in chemistry and biochemistry.

This calculator uses the standard atomic weights published by IUPAC and supports all 118 elements, including complex formulas with parentheses and hydrates.

Understanding Molecular Weight and Molar Mass

Molecular weight (more precisely, relative molecular mass) is the sum of the atomic weights of all atoms in a molecule. It is dimensionless but is often expressed as g/mol when used as molar mass.

Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance. For practical purposes, molecular weight and molar mass are numerically equivalent when expressed in g/mol.

Atomic weight is the weighted average mass of an element's naturally occurring isotopes. For example, chlorine has an atomic weight of 35.45, reflecting a mix of Cl-35 and Cl-37 isotopes.

How to Use the Molecular Weight Calculator

Step 1: Enter Formula: Type the molecular formula using standard chemical notation (e.g., H2O, NaCl, C6H12O6).
Step 2: Or Select Common Chemical: Choose from a dropdown of frequently used compounds.
Step 3: Calculate: The molecular weight is computed instantly, with a breakdown showing each element's contribution.
Step 4: Review Breakdown: See atom counts and individual weights for each element in the compound.

How Molecular Weight is Calculated

Sum of Atomic Weights

MW = Σ (atomic weight × atom count)

Multiply each element's atomic weight by the number of atoms, then sum all contributions.

Example: Water (H₂O)

MW = 2(1.008) + 1(15.999) = 18.015 g/mol

Two hydrogen atoms plus one oxygen atom.

Example: Glucose (C₆H₁₂O₆)

MW = 6(12.011) + 12(1.008) + 6(15.999) = 180.156 g/mol

Six carbons, twelve hydrogens, and six oxygens.

Molecular Weights of Common Compounds

Compound	Formula	Molecular Weight (g/mol)
Water	H₂O	18.015
Sodium Chloride	NaCl	58.44
Glucose	C₆H₁₂O₆	180.156
Sulfuric Acid	H₂SO₄	98.079

Benefits of Our Molecular Weight Calculator

✓
Instant Computation
Enter any formula and get the molecular weight immediately.
✓
All 118 Elements
Full periodic table support using IUPAC standard atomic weights.
✓
Common Compounds
Quick-select dropdown for frequently used chemicals.
✓
Element Breakdown
See the contribution of each element to the total molecular weight.

Frequently Asked Questions

Is molecular weight the same as molar mass?

They are numerically equivalent when expressed in g/mol, but technically, molecular weight is a dimensionless ratio while molar mass has units of g/mol.