Molar Mass Calculator
Type a chemical formula (e.g., H2O, NaCl, C6H12O6, CuSO4.5H2O) to calculate its molar mass, see a per-element breakdown, and view a live 3D atom cluster.
Reviewed by the ToolNestr Editorial Team — July 2026
Enter a chemical formula to calculate its molar mass
Two ideas that trip students up
1. A molecule is a cluster of atoms
A water-style cluster of spheres, sized and coloured by element. It is illustrative only — not to scale and not a real molecular structure — but it shows why molar mass is a property of the whole group, not one atom.
2. Molar mass is just a sum of parts
Each stacked block represents one element's mass contribution (count × atomic mass) for H₂O. Stack them up and the total height is the molar mass — addition, nothing more.
Molar mass graphs
How it works
The core idea in one line: molar mass is just addition — multiply each element's atomic mass by how many times it appears in the formula, then sum every element.
M = Σ(ni × Ai)
sum of atomic mass × count, over every element i
Ai = weighted average
from an element’s naturally occurring isotopes (IUPAC)
mol = mass / M
rearranged to convert grams ↔ moles
Rearranged, the same idea converts grams to moles and back: mol = mass / M. Parentheses multiply everything inside a group, and the dot in a hydrate formula (like CuSO₄·5H₂O) simply adds a separate group's atoms to the total.
Worked example 1 — glucose
Given: Calculate the molar mass of glucose, C₆H₁₂O₆.
Worked example 2 — a hydrate
Given: Calculate the molar mass of copper(II) sulfate pentahydrate, CuSO₄·5H₂O.
The dot (or middle dot ·) in a hydrate formula means addition — parse each side separately, then sum.
Molar mass of familiar compounds
Same principle — sum atomic masses × counts — applied to compounds you already know.
| Compound | Formula | Molar mass |
|---|---|---|
| Water | H₂O | 18.02 g/mol |
| Table salt | NaCl | 58.44 g/mol |
| Carbon dioxide | CO₂ | 44.01 g/mol |
| Glucose | C₆H₁₂O₆ | 180.16 g/mol |
| Sulfuric acid | H₂SO₄ | 98.08 g/mol |
| CuSO₄ pentahydrate | CuSO₄·5H₂O | 249.69 g/mol |
Values rounded to 2 decimal places from IUPAC standard atomic weights.
Where molar mass actually matters
🧪 Chemistry student
Check homework and verify manual molar mass calculations. The breakdown feature shows the contribution of each element, helping you learn the pattern for different compound types.
🧫 Lab technician
Prepare solutions of exact molarity by first calculating the molar mass of the solute. This ensures accurate concentration measurements for experiments and quality control.
💊 Pharmacist
Calculate the molar mass of active pharmaceutical ingredients to determine correct dosages and compounding ratios. Ensure medication formulations meet regulatory specifications.
📊 Materials scientist
Determine the molar mass of polymers, coordination compounds, and novel materials. Use the breakdown to understand the composition and properties of synthesized compounds.
Common misconceptions
"Molar mass and molecular weight are totally different things."
They are numerically the same for molecular compounds — both add up atomic masses over a formula. Molar mass carries units of g/mol; molecular weight (relative molecular mass) is technically unitless, but in everyday lab use the two terms and numbers are interchangeable.
"Atomic mass and molar mass are the same measurement."
Atomic mass is the mass of one atom (in atomic mass units, u) for a single element. Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance, in g/mol. Numerically they match per element because 1 u/atom scales to 1 g/mol — but atomic mass describes one atom, molar mass describes a mole of atoms, molecules, or formula units.
"The dot in a hydrate formula means multiplication of everything."
The dot (or ·) only adds the water molecules to the anhydrous formula's total — it does not multiply the whole compound. CuSO₄·5H₂O is CuSO₄ plus 5 separate H₂O molecules, summed.
"Case doesn't matter when typing element symbols."
It does: "Co" is cobalt, but "CO" is carbon monoxide (carbon + oxygen). Element symbols are always capital-first, lowercase-second (if a second letter exists) — mixing up case changes the formula's meaning entirely.
Formula sources & further reading
The formulas here are standard, traceable to:
- • IUPAC, Standard Atomic Weights — the atomic mass values used throughout this calculator, periodically revised by the Commission on Isotopic Abundances and Atomic Weights. iupac.org
- • OpenStax, Chemistry 2e — formula mass and the mole concept (free, peer-reviewed). openstax.org
- • Brown, LeMay & Bursten, Chemistry: The Central Science — Chapter 3, Stoichiometry: Calculations with Chemical Formulas and Equations.
Molar mass = Σ(atomic mass × atom count) over every element in the formula. Results are rounded for display.
How to use this calculator
Type the formula
Enter any valid chemical formula using standard element symbols. Use parentheses for polyatomic groups, e.g. Ca(OH)2 or Al2(SO4)3.
View the breakdown
The calculator shows a per-element breakdown of atomic count and mass contribution, and updates the 3D atom cluster live.
Check for errors
Invalid element symbols or malformed formulas are caught with a clear error message. All 118 elements are supported with IUPAC-standard atomic weights.
Related tools
Frequently asked questions
What is molar mass?
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in a chemical formula.
How is molar mass calculated?
Multiply each element's atomic mass by its subscript in the formula, then sum. For example, H₂O: (2 × 1.008) + (1 × 16.00) = 18.016 g/mol.
What is a mole?
A mole is Avogadro's number (6.022 × 10²³) of particles — atoms, molecules, or formula units. One mole of any substance has a mass in grams equal to its molar mass.
What elements do you support?
All 118 known elements from Hydrogen to Oganesson, using standard atomic weights from IUPAC. The calculator correctly handles parentheses and hydrated compounds like CuSO₄·5H₂O.
Why is molar mass important in chemistry?
Molar mass is essential for converting between mass and moles, preparing solutions of known concentration, determining empirical formulas, and performing stoichiometric calculations in chemical reactions.