Molecular Weight Calculator
Calculate the molecular weight of any chemical formula using IUPAC 2021 standard atomic weights. Enter formulas with parentheses, brackets, and hydrate notation — the molecular weight calculator parses them instantly and shows a full element breakdown with percentage composition. All 118 elements supported, running locally in your browser with no signup required.
Enter any chemical formula to calculate its molecular weight using IUPAC 2021 standard atomic weights. Supports parentheses, brackets, hydrates (·), and all 118 elements. All calculations run locally in your browser with no signup required.
Use standard notation: element symbols with subscript numbers, parentheses for groups, · or . for hydrates.
Examples
Why Use Our Molecular Weight Calculator?
Accurate, private, and fully browser-based molecular weight calculation online
Instant Molecular Weight Calculation
Calculate the molecular weight of any chemical formula instantly using IUPAC 2021 standard atomic weights. The molecular weight calculator parses complex formulas with parentheses, brackets, and hydrate notation in milliseconds.
Secure Molecular Weight Calculator Online
The molecular weight calculator runs entirely in your browser. Your chemical formulas and calculation results never leave your device — no server, no account, no tracking. Your research stays completely private.
Molecular Weight Calculator - No Installation
Use the molecular weight calculator directly in any modern browser with no downloads, apps, or plugins required. Supports all 118 elements, nested parentheses, and hydrate dot notation — no chemistry software needed.
100% Free with Full Element Coverage
The molecular weight calculator is completely free with no signup, no usage limits, and no ads. Calculate molecular weights for any formula — from simple compounds like H2O to complex organic molecules and coordination compounds.
Common Use Cases for Molecular Weight Calculator
Practical applications of the molecular weight calculator in chemistry and science
Stoichiometry Calculations
Use the molecular weight calculator to find the molar mass of reactants and products before performing stoichiometry calculations. Knowing the molecular weight lets you convert between grams and moles accurately.
Solution Preparation
Chemists use the molecular weight calculator to determine how many grams of a compound to weigh out when preparing solutions of a specific molar concentration. Enter the formula, get the molecular weight, then calculate the required mass.
Empirical and Molecular Formula Verification
Use the molecular weight calculator to verify that a proposed molecular formula matches an experimentally determined molecular weight. Compare the calculated value against mass spectrometry or other analytical data.
Pharmaceutical and Drug Calculations
Pharmacists and pharmaceutical chemists use the molecular weight calculator to calculate drug dosages, convert between mass and molar quantities, and verify the molecular weight of active pharmaceutical ingredients.
Polymer and Materials Science
Materials scientists use the molecular weight calculator to determine the repeat unit molecular weight of polymers and calculate degree of polymerisation. The element breakdown shows the exact composition of complex monomers.
Teaching and Student Use
Chemistry students use the molecular weight calculator to check their manual calculations and learn how atomic weights contribute to molecular weight. The element breakdown table shows each element's contribution and percentage composition.
Understanding the Molecular Weight Calculator
How the molecular weight calculator works and what the results mean
What is Molecular Weight?
Molecular weight (also called molar mass) is the sum of the atomic weights of all atoms in a chemical formula, expressed in grams per mole (g/mol) or equivalently in daltons (Da). It is one of the most fundamental quantities in chemistry, used in stoichiometry, solution preparation, spectroscopy, and pharmaceutical calculations. Our molecular weight calculator uses IUPAC 2021 standard atomic weights — the most current internationally accepted values — for all 118 elements. The calculator supports any valid chemical formula including nested parentheses (e.g. Fe₂(SO₄)₃), square brackets (e.g. [Cu(NH₃)₄]SO₄), and hydrate dot notation (e.g. CuSO₄·5H₂O). All calculations run entirely in your browser with no data sent to any server.
How Our Molecular Weight Calculator Works
- Enter Your Chemical Formula: Type any chemical formula into the input field using standard chemical notation — uppercase for element symbols, lowercase for the second letter, numbers for subscripts. Use parentheses or brackets for groups and a dot (·) for hydrates. Press Enter or click Calculate.
- Instant Browser-Based Parsing:The molecular weight calculator parses your formula using a recursive descent parser that handles nested groups, subscripts, and hydrate coefficients. It looks up each element's atomic weight from the built-in IUPAC 2021 database. Your formula never leaves your device.
- Read Your Results:The calculator shows the total molecular weight in g/mol, a full element breakdown table with each element's atomic number, atomic weight, count, contribution, and percentage composition, plus summary statistics for unique elements and total atom count.
What the Molecular Weight Calculator Shows
- Molecular Weight (g/mol): The total molar mass of the compound, calculated as the sum of (atomic weight × count) for every element in the formula. Displayed to 4 decimal places for precision.
- Element Breakdown Table: Each unique element in the formula with its symbol, full name, atomic number, standard atomic weight, atom count, mass contribution, and percentage of total molecular weight.
- Percentage Composition: The mass percentage of each element shown as both a number and a visual bar, making it easy to see which elements dominate the molecular weight.
- Summary Statistics: Total unique element count, total atom count, and molecular weight in both g/mol and Da (daltons) — 1 Da = 1 g/mol by definition.
Supported Formula Notation
The molecular weight calculator supports the full range of standard chemical formula notation. Simple formulas like H₂O and NaCl work directly. Parentheses for ionic groups: Ca(OH)₂, Fe₂(SO₄)₃. Square brackets for coordination compounds: [Cu(NH₃)₄]SO₄. Hydrate notation using a dot, middle dot (·), or asterisk: CuSO₄·5H₂O, MgSO₄·7H₂O. Nested groups are fully supported. Element symbols must use correct capitalisation — the first letter uppercase and the second letter (if any) lowercase, e.g. Fe not FE or fe. Unknown element symbols return a clear error message identifying the unrecognised symbol.
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Frequently Asked Questions About Molecular Weight Calculator
Common questions about the molecular weight calculator and chemical formula notation
A molecular weight calculator calculates the molar mass of a chemical compound from its formula by summing the atomic weights of all atoms. Our molecular weight calculator uses IUPAC 2021 standard atomic weights for all 118 elements, supports parentheses, brackets, and hydrate notation, and shows a full element breakdown — no signup required.
The molecular weight calculator uses IUPAC 2021 standard atomic weights — the most current internationally accepted values. These are the same values used in the IUPAC periodic table and recommended for all chemical calculations. For radioactive elements with no stable isotopes, the mass number of the most stable isotope is used.
Absolutely. The molecular weight calculator runs entirely in your browser. Your chemical formulas and calculation results are never sent to any server, stored in a database, or tracked. Everything stays completely private on your device.
Yes — the molecular weight calculator is 100% free with no signup, no account, and no usage limits. Calculate molecular weights for as many formulas as you need, completely free forever with no ads.
The molecular weight calculator supports standard chemical notation including: simple formulas (H2O, NaCl), parentheses for ionic groups (Ca(OH)2, Fe2(SO4)3), square brackets for coordination compounds ([Cu(NH3)4]SO4), hydrate dot notation (CuSO4·5H2O), and nested groups. Element symbols must use correct capitalisation (Fe, not FE or fe).
Molecular weight and molar mass are numerically identical and often used interchangeably. Strictly speaking, molecular weight is dimensionless (a ratio relative to 1/12 the mass of carbon-12), while molar mass has units of g/mol. In practice, both refer to the same value — the mass of one mole of a substance in grams.
They are the same thing. Molecular formula weight (or formula weight) is the sum of atomic weights of all atoms in the formula unit. For molecular compounds, this equals the molecular weight. For ionic compounds like NaCl, the term "formula weight" is technically more correct since there are no discrete molecules, but the calculation is identical.
Use a dot (.), middle dot (·), or asterisk (*) to separate the anhydrous formula from the water of crystallisation. For example: CuSO4·5H2O for copper(II) sulfate pentahydrate, or MgSO4·7H2O for Epsom salt. The number before H2O is the hydration coefficient. The molecular weight calculator handles all three separator characters.
Common errors include: unrecognised element symbols (check capitalisation — Fe not FE), unmatched parentheses or brackets, or invalid characters. The error message identifies the specific problem. Make sure element symbols use correct capitalisation: first letter uppercase, second letter (if any) lowercase.