Molecular Weight Calculator

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Molecular Weight Calculator

Molecular Weight Calculator

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

Chemical Formula

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.

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.

Search Elements

Showing 118 of 118 elements

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

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:

Parsing the formula: Identifying each element and its count in the molecule
Looking up atomic weights: Using the standard atomic weights from the periodic table
Calculating contributions: Multiplying each element's atomic weight by its count
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.