Molar Mass Calculator
Calculate molar mass, molecular weight, and elemental composition from any chemical formula. This free molecular weight calculator runs entirely in your browser and shows every step of the calculation.
How to Use the Molar Mass Calculator
Step 1
Enter a chemical formula
Type one formula: H2O, NaCl, or Ca(NO3)2. Parentheses, square brackets, and hydrates such as CuSO4·5H2O all work. Formulas only — to balance a whole reaction, use the equation balancer instead.
Step 2
Click Calculate Molar Mass
The calculator expands the formula into atoms — including everything inside parentheses and hydrate waters — multiplies each count by the IUPAC standard atomic weight, and adds the contributions. Everything runs in your browser; nothing is uploaded.
Step 3
Review the result
Read the molar mass in g/mol, the molecular or formula weight, the atom counts, the elemental composition with mass percentages, the formula breakdown, and the step-by-step calculation. Copy the result for homework or lab notes.
How to Calculate Molar Mass
The molar mass of a substance is the mass of one mole of it — the sum of every atom's atomic weight in the formula. Here is the whole procedure, worked through sulfuric acid. The same five steps cover anything from NaCl to C6H12O6 — the formula changes, the procedure does not.
Step 1Write the chemical formula
Start from the correct formula, subscripts included. Sulfuric acid is H2SO4 — not HSO4 or H2SO3, which are different substances with different molar masses. Hydrates must keep their water: CuSO4·5H2O entered without the ·5H2O gives the anhydrous salt's mass, 90.075 g/mol short.
Step 2Count each atom
Tally every element, multiplying subscripts through parentheses and brackets. H2SO4 holds 2 H, 1 S, and 4 O. In Ca(NO3)2 the subscript 2 multiplies the whole nitrate group, giving 1 Ca, 2 N, and 6 O — and in [Cu(NH3)4]SO4 the subscript 4 multiplies everything inside the brackets. Hydrate waters count too: CuSO4·5H2O totals 21 atoms once its 10 H and 5 O are added.
Step 3Find each atomic weight
Look up the atomic weight of every element on the periodic table. For H2SO4: H = 1.008, S = 32.06, O = 15.999. These IUPAC standard values are already built into the calculator above — and most are not whole numbers because they average an element's naturally occurring isotopes.
Step 4Multiply atomic weight × atom count
Each element contributes its atomic weight once per atom: 2 × 1.008 = 2.016 for hydrogen, 1 × 32.06 = 32.06 for sulfur, and 4 × 15.999 = 63.996 for oxygen. For the nitrate example: 2 × 14.007 = 28.014 and 6 × 15.999 = 95.994.
Step 5Add the results
Sum the contributions: 2.016 + 32.06 + 63.996 = 98.072. One mole of H2SO4 — 6.022 × 10²³ molecules — weighs 98.072 grams, written 98.072 g/mol. Report the total to the same precision as the atomic weights you used; the calculator keeps three decimals.
Where students lose marks
Subscripts inside parentheses apply to every element in the group: Ca(NO3)2 contains six oxygens, not two. If your total is off, expand the formula first — the Formula Breakdown in the result shows exactly that expansion.
Molar Mass vs Molecular Weight
The terms overlap because they describe the same underlying quantity from different angles — per mole versus per molecule.
| Term | Meaning | Typical expression |
|---|---|---|
| Molar mass | Mass of one mole of a substance | g/mol |
| Molecular mass | Mass of one molecule | u / Da |
| Molecular weight | Relative molecular mass; the widely used practical term | Often treated as unitless |
| Formula mass | Sum of atomic masses in a formula unit | u / Da |
Molecular Mass
Molecular mass is the mass of a single molecule, in unified atomic mass units (u) or daltons (Da). One water molecule has a molecular mass of 18.015 u. One molecule is far too light to weigh on a balance, so laboratory work always converts to the per-mole scale.
Formula Mass
Ionic compounds such as NaCl or Ca(NO3)2 do not form discrete molecules — they form crystal lattices of ions. Their mass is reported per formula unit as the formula mass or formula weight, which is why the calculator switches the label for ionic inputs while computing the same number.
Does Molecular Weight Have Units?
Strictly speaking, molecular weight is a relative quantity — a molecule's mass compared with 1/12 of a carbon-12 atom — so it is unitless, while molecular mass carries u or Da. In practice, homework and calculators use "molecular weight" loosely for molar mass, and the values are identical: 58.44 u per NaCl formula unit is 58.44 g/mol.
What Are the Units of Molar Mass?
Molar mass is commonly expressed in grams per mole (g/mol). One mole of water weighs 18.015 g, so water's molar mass is 18.015 g/mol. For very heavy substances the same quantity may be written in kilograms per mole (kg/mol) — 0.018015 kg/mol for water.
Do not confuse this with the atomic mass unit (u, also called the dalton, Da), which describes a single atom or molecule. The two scales mirror each other numerically: a substance with a molecular mass of 18.015 u has a molar mass of 18.015 g/mol. That equality is exactly what makes the mole usable — it turns per-molecule masses into lab-scale grams.
Popular Molar Mass Calculations
The formulas that come up most often in homework sets and labs, each with its own page: molar mass, elemental composition, and the full calculation.
- Carbon DioxideCO₂44.009 g/molA 3-atom linear molecule; carbon is only 27% of the mass.
- Sodium ChlorideNaCl58.44 g/molThe textbook ionic compound — 1 Na and 1 Cl per formula unit, no discrete molecules.
- WaterH₂O18.015 g/mol3 atoms; the two hydrogens contribute just 11% of the mass.
- Calcium CarbonateCaCO₃100.086 g/molLimestone and chalk; the 3 oxygens carry nearly half the mass.
- Sulfuric AcidH₂SO₄98.072 g/mol7 atoms in total; oxygen accounts for about two-thirds of the mass.
- Calcium ChlorideCaCl₂110.978 g/mol1 Ca + 2 Cl; chlorine makes up nearly two-thirds of the mass.
- MethaneCH₄16.043 g/molThe simplest hydrocarbon — 5 atoms, 75% carbon by mass.
- HydrogenH₂2.016 g/molA diatomic element with the smallest molar mass of any substance.
- GlucoseC₆H₁₂O₆180.156 g/mol24 atoms per molecule; oxygen dominates the mass at 53%.
- Calcium OxideCaO56.077 g/molQuicklime — calcium and oxygen in a 1 : 1 formula unit.
Related Chemistry Calculators
Keep working the problem with the other free tools on this site. The molar mass you just found is the conversion factor between grams and moles in every stoichiometry calculation.
- Grams to Moles CalculatorConvert grams ↔ moles with the molar mass you just found.
- Stoichiometry CalculatorConvert between moles, mass, and reaction amounts.
- Empirical Formula CalculatorTurn percent composition into a formula.
- Limiting Reactant CalculatorFind the limiting reagent and theoretical yield.
- Chemical Equation BalancerBalance equations with coefficients and atom checks.
- Lewis Structure GeneratorDraw Lewis dot structures with formal charges.
Frequently Asked Questions
What is a molar mass calculator?
A molar mass calculator converts a chemical formula into the mass of one mole of that substance, expressed in grams per mole. You type a formula such as H2O or Ca(NO3)2, and the calculator counts the atoms, multiplies each count by the element's atomic weight, and adds the contributions — also returning the elemental composition, mass percentages, and the full calculation.
How do I calculate molar mass from a chemical formula?
Count how many atoms of each element the formula contains, look up each element's atomic weight, multiply count × atomic weight for every element, then add the results. For Ca(NO3)2: 1 Ca + 2 N + 6 O gives 40.078 + 28.014 + 95.994 = 164.086 g/mol. The calculator above does this automatically and shows each step.
What is the difference between molar mass and molecular weight?
Molar mass is the mass of one mole of a substance, in g/mol. Molecular weight (strictly, molecular mass) is the mass of one molecule, in atomic mass units (u) or daltons (Da). The two numbers are numerically identical — water is 18.015 g/mol as a molar mass and 18.015 u per molecule — because a mole is defined so that the units match.
What units are used for molar mass?
The standard unit is grams per mole (g/mol). Larger-scale work sometimes uses kilograms per mole (kg/mol). Per single particle, the same quantity is expressed in unified atomic mass units (u) or daltons (Da) — 1 g/mol corresponds to 1 u per formula unit.
Can this calculator handle parentheses in chemical formulas?
Yes. Subscripts outside parentheses multiply everything inside them: Ca(NO3)2 expands to 1 Ca, 2 N, and 6 O, and Al2(SO4)3 expands to 2 Al, 3 S, and 12 O. Square brackets for coordination compounds, such as [Cu(NH3)4]SO4, work as well.
Can the calculator handle hydrates?
Yes. Write the water of crystallization after a dot: CuSO4·5H2O (copper(II) sulfate pentahydrate) adds five waters, 5 × 18.015 = 90.075 g/mol, to the anhydrous salt for a total of 249.677 g/mol. You can write the dot as ·, ., or *.