The molar mass of any formula, instantly.
Type a chemical formula and watch its molar mass appear. It handles subscripts, parentheses like Ca(OH)2, and hydrates like CuSO4.5H2O, then breaks down every element by mass and percent.
The formula
Case matters: Co is cobalt, CO is carbon and oxygen.
Enter grams to get moles and molecule count, or enter moles to get the grams to weigh.
What this formula tells you
Percent composition by mass
Which elements carry the weight
The molecule at a glance
Element breakdown
Every element in the formula, how many atoms of it, its atomic weight, the mass it contributes and its share of the total.
| Element | Atoms | Atomic weight | Total mass | Mass % |
|---|---|---|---|---|
Molecular weight, explained
What Is Molecular Weight?
Molecular weight (or molar mass) is the sum of the atomic weights of all atoms in a molecule, expressed in grams per mole (g/mol). For example, water (H2O) has a molecular weight of 18.015 g/mol: two hydrogen atoms (2 x 1.008) plus one oxygen atom (15.999). Molecular weight is essential for converting between mass and moles in chemistry.
Using Molecular Weight in Calculations
To find the number of moles in a given mass: moles = mass (g) / molecular weight (g/mol). To find the number of molecules: multiply moles by Avogadro's number (6.022 x 10^23). Molecular weight is used in stoichiometry, solution preparation, dosing calculations, and chemical analysis.
Empirical formula vs molecular formula
The molecular formula counts every atom in one molecule, such as glucose C6H12O6. The empirical formula is the same ratio reduced to its smallest whole numbers, which for glucose is CH2O. Both share the same percent composition, but the molecular formula has a molar mass that is a whole-number multiple of the empirical one. Glucose (180.16 g/mol) is exactly six times the empirical CH2O unit (30.03 g/mol). Percent composition alone gives you the empirical formula, you need the measured molar mass to find the true molecular formula.
Common questions
What is the difference between molecular weight and formula weight?
Molecular weight refers to covalent molecules (like H2O or CO2). Formula weight is used for ionic compounds (like NaCl) that do not exist as discrete molecules. Both are calculated the same way by summing atomic weights, but the terminology differs.
What is a mole?
A mole is 6.022 x 10^23 particles (Avogadro's number). One mole of any substance contains this many molecules or formula units. One mole of water (18.015 g) contains 6.022 x 10^23 water molecules.
Why is molecular weight important?
Molecular weight allows chemists to weigh out specific numbers of molecules for reactions. It connects the macroscopic world (grams on a balance) to the microscopic world (individual molecules). Correct stoichiometric calculations depend on accurate molecular weights.
Atomic weights follow the IUPAC standard values and are given to a few decimal places, so results are accurate for classroom and lab-bench work. For high-precision or isotope-specific work, use the exact isotopic masses for your sample.