Atomic Mass u or Da
The mass of an individual atom of an element. Standard atomic weights represent weighted averages of naturally occurring isotopes on Earth.
IUPAC 118 Elements • Parentheses & Hydrate Support
Molecular Weight Calculator
Calculate the molecular weight and molar mass of chemical compounds instantly. Enter a chemical formula to view total mass, elemental composition, and detailed calculation results.
Molecular Weight Calculator
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Please check the element symbols, subscripts, and parentheses.
Quick Formula Examples
Click any compound to populate and calculate (common representative names shown)
Molar Mass
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g/mol
Mass of 1 mole ($6.022 \times 10^{23}$ units)
Molecular Weight / Mass
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u (Da)
Relative mass per formula unit
Chemical Formula
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Normalized notation
Atom & Element Count
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atoms
— unique elements
Elemental Composition Breakdown
Elements ordered by first appearance in the entered formula| Element | Name | Atom Count | Atomic Mass (g/mol) | Subtotal (g/mol) | Mass Percentage |
|---|---|---|---|---|---|
| Total | — | — | — | 100.00% | |
Dataset & Isotopic Note: Calculations use IUPAC conventional standard atomic weights. For synthetic or radioactive elements lacking a standard atomic weight, the mass number of a representative longest-lived isotope is used. Values may vary slightly in the final decimal place compared to sources using rounded textbook tables or specific isotopic abundances.
Scientific Methodology
How to Calculate Molecular Weight
Understand the step-by-step stoichiometry principles used by the Molecular Weight Calculator to evaluate chemical compounds and hydrates.
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1
Enter a Chemical Formula
Enter a chemical formula, such as
H2OorC6H12O6, including any parentheses, coordination brackets, or hydration dots. -
2
Element Identification & Atom Counting
The calculator identifies each element and counts its atoms by expanding nested groups and applying stoichiometric hydrate coefficients.
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3
Multiply by Standard Atomic Mass
Each atomic count is multiplied by the corresponding atomic mass from the 118-element IUPAC dataset without premature rounding.
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4
Sum Elemental Contributions
All elemental contributions are added together to determine the total molecular weight and molar mass.
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5
View Complete Breakdown
The final molar mass and elemental composition are displayed alongside mass percentages and downloadable CSV data.
Worked Example: Water (H2O)
Using our implemented atomic mass dataset where Hydrogen ($\text{H}$) = 1.008 g/mol and Oxygen ($\text{O}$) = 15.999 g/mol:
Hydrogen (H): 2 atoms × 1.008 g/mol = 2.016 g/mol
Oxygen (O): 1 atom × 15.999 g/mol = 15.999 g/mol
Total Molar Mass: 2.016 + 15.999 = 18.015 g/mol
Mass % of H: (2.016 / 18.015) × 100% = 11.19%
Mass % of O: (15.999 / 18.015) × 100% = 88.81%
Important Physical Distinction: For neutral compounds, the numerical value of molecular mass in unified atomic mass units ($\text{u}$ or $\text{Da}$) and molar mass in $\text{g/mol}$ is identical (18.015), but they represent different physical scales. One molecule of $\text{H}_2\text{O}$ has a mass of approximately $18.015\text{ u}$ ($\approx 2.9915 \times 10^{-23}\text{ g}$), whereas one mole ($6.02214076 \times 10^{23}$ molecules) has a mass of $18.015\text{ g}$.
Molecular Weight Dimensionless / u
Also called relative molecular mass ($M_r$), defined as the ratio of the mass of a molecule to $1/12\text{th}$ the mass of a carbon-12 atom.
Molecular Mass u or Da
The mass of one single discrete molecule of a covalent compound measured in unified atomic mass units ($\text{u}$) or Daltons ($\text{Da}$).
Molar Mass g/mol
The mass in grams of one mole ($6.02214076 \times 10^{23}$ elementary entities) of any chemical element, molecular compound, or ionic salt.
Formula Mass u or Da
The sum of atomic weights of atoms in the empirical formula unit of an ionic lattice or network solid (such as $\text{NaCl}$ or $\text{CaCO}_3$) that does not exist as discrete molecules.
Engineered for Precision
Key Capabilities of Our Molecular Weight Calculator
Built with a deterministic grammar parser and complete IUPAC atomic dataset for reliable academic, laboratory, and classroom calculations.
Accurate Formula Parsing
Supports common chemical formulas, subscripts, and nested groups including parentheses () and coordination square brackets [].
Instant Calculation
Calculate molecular weight and molar mass directly in your browser with zero latency and full floating-point internal precision.
Elemental Breakdown
View the atom count, atomic mass, mass subtotal, and percentage composition for every unique element in your compound.
Hydrate Support
Calculate formulas containing hydration notation and hydrate coefficients such as CuSO4·5H2O accurately.
Copy and Export
Copy calculation results or download an elemental breakdown in CSV format for lab reports and spreadsheets.
Mobile Friendly
Use the calculator comfortably on desktop, tablet, and smartphone with responsive tables and touch-friendly controls.
Privacy Friendly
Perform calculations locally in the browser without sending formula input to a calculation server.
Questions & Answers
Frequently Asked Questions
Common questions about chemical formula syntax, molar mass units, hydrates, and atomic weight standards.
A molecular weight calculator is a scientific tool that parses a chemical formula, counts the total number of atoms for each chemical element present, and multiplies those counts by their respective standard atomic weights to determine the total molecular weight and molar mass of the substance.
Molecular weight is calculated by summing the atomic masses of all atoms in a chemical formula:
Molecular Mass = Σ (Element Atom Count × Atomic Mass). For example, in water (H2O), 2 hydrogen atoms (2 × 1.008) plus 1 oxygen atom (1 × 15.999) equals 18.015.
Molecular weight (or relative molecular mass) is a dimensionless ratio—or is expressed as molecular mass in unified atomic mass units (
u or Da)—representing the mass of a single molecule relative to 1/12th of a carbon-12 atom. Molar mass represents the mass of one mole ($6.02214076 \times 10^{23}$ entities) of a substance and is expressed in grams per mole (g/mol). While their numerical values are identical for neutral compounds, they measure different physical quantities.
Enter standard case-sensitive element symbols followed by their atom counts, such as
H2O, C6H12O6, or NaCl. Always capitalize the first letter of each element symbol and keep the second letter lowercase (for example, Co for Cobalt versus CO for Carbon Monoxide).
Yes. The built-in recursive descent formula parser supports round parentheses
(), square brackets [], and multi-level nested groups such as Ca(OH)2, Al2(SO4)3, and K4[Fe(CN)6].
Yes. You can enter hydrated compounds using the middle dot symbol (
·) or a period (.) between the anhydrous compound and the water of crystallization, such as CuSO4·5H2O or CuSO4.5H2O. The coefficient preceding the hydrate group multiplies all atoms within that segment.
Minor differences in the third or fourth decimal place occur when different tools use rounded textbook atomic weights (such as
O = 16.00) instead of IUPAC conventional standard atomic weights (such as O = 15.999), or when different representative isotopes are selected for synthetic radioactive elements.
Yes. The parser automatically normalizes Unicode subscript digits (
₀₁₂₃₄₅₆₇₈₉) into standard ASCII digits before evaluating, so formulas copied from scientific articles like H₂O, CO₂, and C₆H₁₂O₆ calculate accurately.
Yes, the Molecular Weight Calculator is completely free to use online for students, teachers, laboratory technicians, and researchers without any account registration.
All chemical formula parsing and molecular weight calculations are executed locally inside your browser using JavaScript; your formula inputs are not transmitted to or stored on any calculation server. Please note that third-party advertising scripts embedded on the page operate independently under their respective network policies.