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Molecular Weight Calculator

Calculate the molecular weight of chemical compounds from their formulas.
Supports complex formulas with parentheses, subscripts, and multiple elements.

Enter a chemical formula using element symbols (e.g., H2O for water, NaCl for salt). Use parentheses for groups like Ca(OH)2.

Note: Use the letter O (oxygen), not the number 0.

Common Compounds

Enter a chemical formula above to calculate the molecular weight

Atomic Weights Reference Table

Reference table showing all elements and their atomic weights (in g/mol) used by this calculator. These values are based on the IUPAC standard atomic weights.

Showing 118 of 118 elements

Ac 227.000 g/mol
Actinium
Ag 107.868 g/mol
Silver
Al 26.982 g/mol
Aluminum
Am 243.000 g/mol
Americium
Ar 39.950 g/mol
Argon
As 74.922 g/mol
Arsenic
At 210.000 g/mol
Astatine
Au 196.967 g/mol
Gold
B 10.810 g/mol
Boron
Ba 137.327 g/mol
Barium
Be 9.012 g/mol
Beryllium
Bh 270.000 g/mol
Bohrium
Bi 208.980 g/mol
Bismuth
Bk 247.000 g/mol
Berkelium
Br 79.900 g/mol
Bromine
C 12.011 g/mol
Carbon
Ca 40.078 g/mol
Calcium
Cd 112.411 g/mol
Cadmium
Ce 140.116 g/mol
Cerium
Cf 251.000 g/mol
Californium
Cl 35.453 g/mol
Chlorine
Cm 247.000 g/mol
Curium
Cn 285.000 g/mol
Copernicium
Co 58.933 g/mol
Cobalt
Cr 51.996 g/mol
Chromium
Cs 132.905 g/mol
Cesium
Cu 63.546 g/mol
Copper
Db 268.000 g/mol
Dubnium
Ds 281.000 g/mol
Darmstadtium
Dy 162.500 g/mol
Dysprosium
Er 167.259 g/mol
Erbium
Es 252.000 g/mol
Einsteinium
Eu 151.964 g/mol
Europium
F 18.998 g/mol
Fluorine
Fe 55.845 g/mol
Iron
Fl 289.000 g/mol
Flerovium
Fm 257.000 g/mol
Fermium
Fr 223.000 g/mol
Francium
Ga 69.723 g/mol
Gallium
Gd 157.249 g/mol
Gadolinium
Ge 72.630 g/mol
Germanium
H 1.008 g/mol
Hydrogen
He 4.003 g/mol
Helium
Hf 178.486 g/mol
Hafnium
Hg 200.592 g/mol
Mercury
Ho 164.930 g/mol
Holmium
Hs 270.000 g/mol
Hassium
I 126.904 g/mol
Iodine
In 114.818 g/mol
Indium
Ir 192.217 g/mol
Iridium
K 39.098 g/mol
Potassium
Kr 83.798 g/mol
Krypton
La 138.905 g/mol
Lanthanum
Li 6.940 g/mol
Lithium
Lr 266.000 g/mol
Lawrencium
Lu 174.967 g/mol
Lutetium
Lv 293.000 g/mol
Livermorium
Mc 290.000 g/mol
Moscovium
Md 258.000 g/mol
Mendelevium
Mg 24.305 g/mol
Magnesium
Mn 54.938 g/mol
Manganese
Mo 95.950 g/mol
Molybdenum
Mt 278.000 g/mol
Meitnerium
N 14.007 g/mol
Nitrogen
Na 22.990 g/mol
Sodium
Nb 92.906 g/mol
Niobium
Nd 144.242 g/mol
Neodymium
Ne 20.180 g/mol
Neon
Nh 286.000 g/mol
Nihonium
Ni 58.693 g/mol
Nickel
No 259.000 g/mol
Nobelium
Np 237.000 g/mol
Neptunium
O 15.999 g/mol
Oxygen
Og 294.000 g/mol
Oganesson
Os 190.230 g/mol
Osmium
P 30.974 g/mol
Phosphorus
Pa 231.036 g/mol
Protactinium
Pb 207.200 g/mol
Lead
Pd 106.420 g/mol
Palladium
Pm 145.000 g/mol
Promethium
Po 209.000 g/mol
Polonium
Pr 140.908 g/mol
Praseodymium
Pt 195.084 g/mol
Platinum
Pu 244.000 g/mol
Plutonium
Ra 226.000 g/mol
Radium
Rb 85.468 g/mol
Rubidium
Re 186.207 g/mol
Rhenium
Rf 267.000 g/mol
Rutherfordium
Rg 282.000 g/mol
Roentgenium
Rh 102.906 g/mol
Rhodium
Rn 222.000 g/mol
Radon
Ru 101.070 g/mol
Ruthenium
S 32.060 g/mol
Sulfur
Sb 121.760 g/mol
Antimony
Sc 44.956 g/mol
Scandium
Se 78.971 g/mol
Selenium
Sg 271.000 g/mol
Seaborgium
Si 28.085 g/mol
Silicon
Sm 150.360 g/mol
Samarium
Sn 118.710 g/mol
Tin
Sr 87.620 g/mol
Strontium
Ta 180.948 g/mol
Tantalum
Tb 158.925 g/mol
Terbium
Tc 98.000 g/mol
Technetium
Te 127.600 g/mol
Tellurium
Th 232.038 g/mol
Thorium
Ti 47.867 g/mol
Titanium
Tl 204.383 g/mol
Thallium
Tm 168.934 g/mol
Thulium
Ts 294.000 g/mol
Tennessine
U 238.029 g/mol
Uranium
V 50.941 g/mol
Vanadium
W 183.840 g/mol
Tungsten
Xe 131.293 g/mol
Xenon
Y 88.906 g/mol
Yttrium
Yb 173.045 g/mol
Ytterbium
Zn 65.380 g/mol
Zinc
Zr 91.222 g/mol
Zirconium

Table of Contents

What is Molecular Weight?

Molecular weight (also called molecular mass or molar mass) is the sum of the atomic weights of all atoms in a molecule. It's expressed in atomic mass units (amu) or grams per mole (g/mol). The molecular weight is crucial in chemistry for stoichiometric calculations, determining the amount of substance in reactions, and understanding molecular properties.

For example, water (H2O) has a molecular weight of approximately 18.015 g/mol, calculated by adding the atomic weights of two hydrogen atoms (2 × 1.008) and one oxygen atom (15.999).

Molecular weight is essential in:

  • Stoichiometry: Calculating reactant and product amounts in chemical reactions
  • Solution preparation: Determining concentrations and molarity
  • Gas laws: Understanding behavior of gases at different conditions
  • Material science: Characterizing polymers and large molecules
  • Pharmaceuticals: Dosage calculations and drug formulation

How it Works

Our molecular weight calculator parses chemical formulas and calculates the total molecular weight by:

  1. Parsing the formula: Identifying each element and its count in the molecule
  2. Looking up atomic weights: Using the standard atomic weights from the periodic table
  3. Calculating contributions: Multiplying each element's atomic weight by its count
  4. Summing the total: Adding all contributions to get the final molecular weight

The calculator handles complex formulas with:

  • Multiple elements (e.g., C6H12O6 for glucose)
  • Subscripts indicating atom counts (e.g., H2O has 2 hydrogen atoms)
  • Parentheses for groups (e.g., Ca(OH)2 has one calcium, two oxygen, and two hydrogen atoms)
  • Nested parentheses for complex structures

All calculations use standard atomic weights from the IUPAC periodic table, ensuring accuracy for scientific and educational purposes.

Formula Format

Chemical formulas should follow standard notation:

Element Symbols

Use standard element symbols (first letter uppercase, second letter lowercase if present). Examples: H (hydrogen), He (helium), Na (sodium), Cl (chlorine).

Subscripts

Numbers after element symbols indicate the count. H2O means 2 hydrogen atoms and 1 oxygen atom. If no number is shown, it's assumed to be 1.

Parentheses

Use parentheses to group atoms. Ca(OH)2 means one Ca atom, and the (OH) group appears twice, giving 2 O atoms and 2 H atoms total.

Examples of Valid Formulas

  • H2O - Water
  • NaCl - Sodium chloride
  • C6H12O6 - Glucose
  • Ca(OH)2 - Calcium hydroxide
  • Al2(SO4)3 - Aluminum sulfate
  • CH3COOH - Acetic acid

Examples

Example 1: Water (H2O)

Formula: H2O

Calculation: 2 × H (1.008) + 1 × O (15.999) = 2.016 + 15.999 = 18.015 g/mol

Result: 18.015 g/mol

Example 2: Glucose (C6H12O6)

Formula: C6H12O6

Calculation: 6 × C (12.011) + 12 × H (1.008) + 6 × O (15.999) = 72.066 + 12.096 + 95.994 = 180.156 g/mol

Result: 180.156 g/mol

Example 3: Calcium Hydroxide (Ca(OH)2)

Formula: Ca(OH)2

Calculation: 1 × Ca (40.078) + 2 × O (15.999) + 2 × H (1.008) = 40.078 + 31.998 + 2.016 = 74.092 g/mol

Result: 74.092 g/mol

Example 4: Aluminum Sulfate (Al2(SO4)3)

Formula: Al2(SO4)3

Calculation: 2 × Al (26.982) + 3 × S (32.065) + 12 × O (15.999) = 53.964 + 96.195 + 191.988 = 342.147 g/mol

Result: 342.147 g/mol

Common Use Cases

  • Chemistry Education: Students learning stoichiometry and molecular calculations
  • Laboratory Work: Preparing solutions with specific molarities and concentrations
  • Chemical Reactions: Calculating reactant and product masses in balanced equations
  • Pharmaceuticals: Determining drug dosages and formulation concentrations
  • Material Science: Characterizing polymers, proteins, and complex molecules
  • Quality Control: Verifying compound purity and composition in manufacturing
  • Research: Analyzing molecular structures and properties in scientific studies
  • Environmental Science: Calculating pollutant concentrations and environmental impact

Frequently Asked Questions

What's the difference between molecular weight and atomic weight?

Atomic weight is the average mass of a single atom of an element, while molecular weight is the sum of atomic weights of all atoms in a molecule. For example, the atomic weight of hydrogen is 1.008 amu, but the molecular weight of H2O (water) is 18.015 g/mol, which includes two hydrogen atoms and one oxygen atom.

How do I enter formulas with parentheses?

Simply type the formula with parentheses as you would write it. For example, Ca(OH)2 for calcium hydroxide or Al2(SO4)3 for aluminum sulfate. The calculator will automatically multiply the contents of parentheses by the number that follows them.

What if my formula has nested parentheses?

The calculator supports nested parentheses. For example, you can enter formulas like (Ca(OH)2)2, though such complex structures are less common. Make sure all opening parentheses have matching closing parentheses.

Are the atomic weights accurate?

Yes, we use standard atomic weights from the IUPAC (International Union of Pure and Applied Chemistry) periodic table. These values are the most current and accurate atomic weights used in scientific calculations. Note that some elements have atomic weights that vary slightly due to isotopic composition, but we use the standard values for consistency.

Can I calculate the molecular weight of ions?

The calculator works with neutral molecular formulas. For ions, you can enter the formula without the charge (e.g., SO4 instead of SO4²⁻), and the molecular weight will be calculated. However, note that the charge doesn't affect the molecular weight calculation itself.

What units are used for molecular weight?

Molecular weight is displayed in grams per mole (g/mol), which is the standard unit in chemistry. This is equivalent to atomic mass units (amu) per molecule, but g/mol is more commonly used in practical calculations involving moles and molarity.

Why does my calculation differ slightly from other sources?

Small differences can occur due to:

  • Different rounding methods (we round to 3 decimal places)
  • Variations in atomic weight values from different periodic table versions
  • Isotopic composition variations in natural elements

Our values should match standard chemistry textbooks and most online calculators within rounding precision.

Can I use this for organic compounds?

Yes! The calculator works with any chemical formula, including organic compounds. Simply enter the formula with proper element symbols and subscripts. For example, C6H12O6 (glucose), CH4 (methane), or C2H5OH (ethanol) all work perfectly.