Molecular Weight Calculator
Calculate molecular weight (molar mass) from chemical formulas. Enter any compound and get instant results with elemental composition breakdown.
Results
Molecular Weight
18.015 g/mol
Enter Chemical Formula
Quick examples:
Molecular Weight of H2O
Molecular Weight
18.015 g/mol
Elemental Composition
| Element | Symbol | Atomic Weight | Count | Mass | % by Mass |
|---|---|---|---|---|---|
| Hydrogen | H | 1.008 | 2 | 2.016 | 11.2% |
| Oxygen | O | 15.999 | 1 | 15.999 | 88.8% |
| Total | 3 | 18.015 | 100% | ||
Common Compounds Reference
| Name | Formula | MW (g/mol) | Action |
|---|---|---|---|
| Water | H2O | 18.015 | |
| Glucose | C6H12O6 | 180.156 | |
| Sodium Chloride | NaCl | 58.44 | |
| Sulfuric Acid | H2SO4 | 98.072 | |
| Ethanol | C2H5OH | 46.069 | |
| Carbon Dioxide | CO2 | 44.009 | |
| Ammonia | NH3 | 17.031 | |
| Acetic Acid | CH3COOH | 60.052 | |
| Calcium Carbonate | CaCO3 | 100.086 | |
| Aspirin | C9H8O4 | 180.159 | |
| Caffeine | C8H10N4O2 | 194.194 | |
| Methane | CH4 | 16.043 |
Common Elements Reference
H
Hydrogen
1.008
He
Helium
4.0026
Li
Lithium
6.94
Be
Beryllium
9.0122
B
Boron
10.81
C
Carbon
12.011
N
Nitrogen
14.007
O
Oxygen
15.999
F
Fluorine
18.998
Ne
Neon
20.18
Na
Sodium
22.99
Mg
Magnesium
24.305
Al
Aluminum
26.982
Si
Silicon
28.085
P
Phosphorus
30.974
S
Sulfur
32.06
Cl
Chlorine
35.45
Ar
Argon
39.948
Formula Entry Tips
Basic Formulas
- •
H2O- Water - •
NaCl- Sodium chloride - •
CO2- Carbon dioxide - •
NH3- Ammonia
With Parentheses
- •
Ca(OH)2- Calcium hydroxide - •
Mg(NO3)2- Magnesium nitrate - •
Al2(SO4)3- Aluminum sulfate
Quick Answer
Molecular weight (MW) is the sum of atomic masses of all atoms in a molecule. Enter a chemical formula like H2O: H (1.008) x 2 + O (16.00) = 18.016 g/mol. For NaCl: Na (22.99) + Cl (35.45) = 58.44 g/mol. For glucose C6H12O6: 6(12.01) + 12(1.008) + 6(16.00) = 180.16 g/mol.
Key Facts
- Molecular weight = sum of all atomic masses in molecule
- Units: g/mol (grams per mole)
- H = 1.008, C = 12.01, N = 14.01, O = 16.00
- Na = 22.99, Cl = 35.45, Ca = 40.08
- Water H2O = 18.02 g/mol
- NaCl = 58.44 g/mol
- Glucose C6H12O6 = 180.16 g/mol
- 1 mole of any compound weighs its MW in grams
Frequently Asked Questions
Molecular weight is calculated by adding the atomic weights of all atoms in the molecule. For H2O: (2 × 1.008) + 15.999 = 18.015 g/mol. Multiply each element's atomic weight by its subscript count, then sum all contributions.
They are numerically equal but have different units. Molecular weight (MW) is dimensionless (based on atomic mass units), while molar mass is expressed in g/mol. For practical chemistry, they can be used interchangeably.
Use standard chemical notation: element symbols with subscript numbers. Examples: H2O (water), NaCl (salt), C6H12O6 (glucose), Ca(OH)2 (calcium hydroxide). Parentheses with subscripts are supported.
Molecular weight is essential for stoichiometry calculations, determining moles from mass, calculating concentrations, and understanding reaction ratios. It connects the microscopic (molecules) to macroscopic (grams) world.
Atomic weights are based on the weighted average of naturally occurring isotopes, expressed relative to carbon-12 (defined as exactly 12). Values come from IUPAC (International Union of Pure and Applied Chemistry).
Results
Molecular Weight
18.015 g/mol