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Molecular Weight Calculator

Molar mass from a chemical formula, element by element.

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Case matters — Co is cobalt, CO is carbon monoxide. Parentheses and nested groups are supported.

Element breakdown

ElementAtomsAtomic weightContributes% by mass

Grams to moles

Molecular weight

—

Details

Distinct elements—
Total atoms—
Heaviest element—
Mass of 1 mole—

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Molecules in the mass you entered

Molar mass is the bridge between the mass you can weigh and the moles a reaction consumes, which makes it the first step in nearly every stoichiometry problem. Atomic weights are the IUPAC standard values.

Quick Tool Overview

The Molecular Weight Calculator parses a chemical formula — including parentheses and nested groups — and returns its molar mass with every element's contribution, the percentage composition by mass, and a grams-to-moles converter.

What it does
Calculates molar mass and composition from a formula
You give it
A chemical formula such as Ca(OH)2 or Al2(SO4)3
You get back
Molar mass, per-element breakdown and percentages
Best for
Stoichiometry, lab prep and chemistry homework
Calculators Free, unlimited use No sign-up Runs in your browser

About the Molecular Weight Calculator

Type a chemical formula and get its molecular weight in grams per mole, with each element's contribution broken out. Parentheses and nested groups are parsed, so Ca(OH)₂ and Al₂(SO₄)₃ are both handled correctly.

The percentage composition by mass is calculated alongside, which is the figure that answers what fraction of a fertiliser is actually nitrogen or how much of a hydrate is water. Because molar mass is the bridge between the mass you can weigh and the moles a reaction actually consumes, it is the first calculation in almost every stoichiometry problem — so a grams to moles converter is included on the same page.

Key features of the Molecular Weight Calculator

Parses nested groups

Parentheses and multipliers are handled, so Al2(SO4)3 works as written.

Per-element breakdown

Each element atom count, atomic weight and contribution to the total.

Percentage composition

The mass fraction of each element — what fraction of a fertiliser is actually nitrogen.

Grams to moles built in

Because molar mass is the bridge between what you weigh and what reacts.

Case sensitivity respected

Co is cobalt and CO is carbon monoxide, and the parser treats them as different.

How to use the Molecular Weight Calculator

  1. 1

    Type a formula

    Case matters: Co is cobalt and CO is carbon monoxide. Parentheses and nested groups work.

  2. 2

    Read the molar mass

    In grams per mole, with each element contribution listed.

  3. 3

    Check the composition

    Percentage by mass for each element in the compound.

  4. 4

    Convert grams to moles

    Enter a mass and see the number of moles it represents.

Frequently asked questions

Add the atomic weight of every atom in the formula. Water, H₂O, is 2 × 1.008 + 15.999 = 18.015 grams per mole.

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