Type a formula — from O₂ to CuSO₄·5H₂O — and get the exact molar mass, elemental breakdown, and percent composition in real time. No sign-up, no guesswork.
Supports parentheses, hydrates (use a dot, e.g. CuSO4.5H2O) and multi-digit subscripts.
| Element | Symbol | Count | Atomic mass | Total mass | % Composition |
|---|
Use the calculated molar mass to find molarity from a mass and volume.
Every feature is designed to make molecular weight calculations fast, transparent and mistake-proof.
All 118 elements with precise IUPAC atomic masses baked in — no external lookups required.
Correctly parses groups like Al₂(SO₄)₃ and complex hydrates such as CuSO₄·5H₂O.
Calculations run entirely in your browser in under 10 milliseconds — nothing is sent to a server.
See exactly how much each element contributes to total mass, with a visual breakdown bar.
Feed in a solute mass and solution volume to get molar concentration without leaving the page.
Instant feedback on malformed formulas, unknown symbols, or unbalanced brackets as you type.
Copy results to your clipboard or download a plain-text report for lab notebooks and reports.
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Enter the chemical formula exactly as written, e.g. C6H12O6 or Ca(OH)2.
The engine tokenizes elements, subscripts, parentheses and hydrate dots into a structured atom count.
Each atom's IUPAC standard atomic weight is multiplied by its count and totalled instantly.
Molar mass, percent composition and molarity tools appear — ready to copy or download.
Every chemistry student eventually runs into the same wall: a formula on a worksheet and no easy way to check whether the arithmetic behind it is right. A molar mass calculator solves that problem by turning a written formula into a precise number of grams per mole, instantly and without a periodic table chart pinned to the wall. That number — the molar mass — is simply the mass of one mole of a substance, and it is the bridge between the microscopic world of atoms and the macroscopic world of grams sitting on a lab balance.
Molar mass is the mass, in grams, of 6.022 × 10²³ particles (Avogadro's number) of a given substance. It is often used interchangeably with "molecular weight," although chemists sometimes reserve the latter term for the dimensionless ratio and the former for the value expressed in g/mol. In practice, both describe the same underlying calculation: add up the atomic mass of every atom present in a formula, accounting for how many times each one appears.
Oxygen is one of the most frequently looked-up entries in any chemistry reference, and for good reason — it appears in water, carbon dioxide, glucose, and thousands of other compounds. A single oxygen atom has an atomic mass of roughly 16.00 g/mol, but molecular oxygen as it exists in air, O₂, has a molar mass close to 32.00 g/mol because two atoms are bonded together. This distinction between atomic mass and molecular mass trips up a lot of newcomers, and it is exactly the kind of detail this tool handles automatically.
Finding molar mass by hand follows a repeatable pattern. First, identify every distinct element in the formula. Second, note how many atoms of each element are present, paying close attention to subscripts and to numbers that apply to an entire group in parentheses. Third, multiply each element's standard atomic weight by its atom count. Finally, add all of those products together to get the total molar mass in grams per mole. For a compound like calcium hydroxide, Ca(OH)₂, that means multiplying the combined mass of one oxygen and one hydrogen by two, then adding the mass of a single calcium atom.
A molecular weight calculator does exactly what was just described, only faster and with no risk of a misread digit or a forgotten parenthesis. This matters most for longer formulas — hydrates such as copper sulfate pentahydrate, coordination compounds, or organic molecules with dozens of atoms — where a single arithmetic slip changes the final answer. Using an automated tool also frees up mental energy for the actual chemistry: understanding why a reaction proceeds the way it does, rather than re-checking long division.
Molar mass is also the starting point for one of the most common calculations in a wet lab: molarity, or molar concentration. Once the molar mass of a solute is known, dividing a measured mass by that value gives the number of moles present. Dividing moles by the volume of solution, expressed in liters, then gives molarity in mol/L. A calculator molarity workflow like the one built into this page removes an entire step from that process, letting a student or technician move directly from formula to concentration without switching tools or reaching for a separate reference.
Seeing a few familiar compounds side by side helps build intuition for what "reasonable" molar mass values look like, and makes it easier to spot an error if a calculated result seems far too high or low.
| Formula | Name | Molar mass (g/mol) |
|---|---|---|
| H₂O | Water | 18.015 |
| CO₂ | Carbon dioxide | 44.009 |
| NaCl | Sodium chloride (table salt) | 58.44 |
| C₆H₁₂O₆ | Glucose | 180.156 |
| CaCO₃ | Calcium carbonate | 100.087 |
| H₂SO₄ | Sulfuric acid | 98.079 |
| NH₃ | Ammonia | 17.031 |
Beyond the classroom, molar mass underpins dosing in pharmacology, stoichiometric planning in industrial chemistry, recipe scaling in food science, and quality control in materials manufacturing. Anywhere a recipe calls for a specific number of moles rather than a specific number of grams, molar mass is the conversion factor that makes the instruction usable on a lab bench. Understanding it well — and having a fast, reliable tool to check it — is one of the most transferable skills a chemistry student can build.
Add up the atomic masses of every atom in the chemical formula, multiplying each element's atomic mass by the number of times it appears. The sum, expressed in grams per mole (g/mol), is the molar mass. This calculator automates that process for any formula you type in.
Multiply the atomic mass inside the parentheses by the subscript that follows them, then add the mass of any atoms outside the parentheses. For Ca(OH)₂, that means calcium plus two times the combined mass of one oxygen and one hydrogen atom.
Divide the mass of solute in grams by its molar mass to get the number of moles, then divide the moles by the solution's volume in liters. The result is molar concentration, expressed in mol/L. Try it in the molarity box after calculating a formula above.
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