Molar Mass Calculator

Quick Answer

Last updated: 3 November 2026 ·How we calculate this: standard atomic weights

How This Molar Mass Calculator Works

Type a chemical formula such as NaCl, Ca(OH)2 or CuSO4·5H2O. The calculator reads each element symbol and its count, multiplies out brackets and hydrate parts, and adds up the atomic weights. It shows the molar mass in grams per mole, each element’s share of the mass, and, if you enter a sample mass, how many moles and molecules it holds.

How to Use the Molar Mass Calculator

1. Type the chemical formula, using capital letters correctly.
2. Use brackets for groups and a dot or * for hydrates.
3. Optionally enter a sample mass in grams.
4. Press Calculate.
5. Read the molar mass, the steps and the element breakdown.

Core Formulas

• Molar mass: M = Σ (number of atoms × atomic weight)
• Moles: n = mass ÷ molar mass
• Mass: mass = moles × molar mass
• Mass percent: element mass ÷ molar mass × 100
• Particles: moles × 6.02214076 × 10²³

Key Terms

• Molar mass: the mass of one mole of a substance, in g/mol.
• Atomic weight: the average mass of an element’s atoms as found in nature.
• Mole: an amount equal to 6.02214076 × 10²³ particles.
• Hydrate: a compound with water molecules built into its crystals.
• Mass percent: the share of a compound’s mass that comes from one element.

Worked Example

Find the molar mass of copper(II) sulfate pentahydrate, CuSO₄·5H₂O.

• CuSO₄ = 63.546 + 32.06 + 4 × 15.999 = 159.602 g/mol
• 5H₂O = 5 × 18.015 = 90.075 g/mol
• Total = 249.677 g/mol

Real-Life Examples

• Lab prep: to make 1 mol of NaCl, weigh out 58.44 g.
• Moles from mass: 50 g of CaCO₃ is 0.4996 mol.
• Percent composition: water is 11.19% hydrogen and 88.81% oxygen by mass.
• Solutions: use the molar mass with our Molarity Calculator to make solutions.

Molar Mass vs Molecular Weight

• Molar mass: mass per mole, in g/mol.
• Molecular weight: mass of one molecule, in daltons (Da) or u.
• Same number: water is 18.015 g/mol and 18.015 Da.

Molar Masses of Common Compounds

Tips for Typing Formulas

• Capitals matter: Co is cobalt, but CO is carbon and oxygen.
• Brackets: Mg(OH)2 has 2 oxygen and 2 hydrogen atoms.
• Hydrates: use a dot or *, such as MgSO4*7H2O.
• Subscripts: type them as normal numbers. H₂O and H2O both work.

Using Molar Mass in Reactions

Molar mass is the bridge between the grams you weigh on a scale and the moles in a balanced equation. To find how much product a reaction can make, change grams of the starting substance to moles, use the equation’s ratio, then change moles back to grams with the product’s molar mass.

• Example: 2H₂ + O₂ → 2H₂O. Burning 4.032 g of hydrogen (2 mol) gives 2 mol of water.
• Grams of water: 2 mol × 18.015 g/mol = 36.030 g.
• Limiting reactant: work out moles of each starting substance to see which runs out first.

The same steps help with dosing, cooking chemistry and lab recipes. Always keep the units in your working, grams on top and moles below, so they cancel the right way and you can spot mistakes quickly.

Common Mistakes to Avoid

• Wrong capitals. NaCl, not NACL or nacl.
• Forgetting bracket counts. In Al2(SO4)3 there are 12 oxygen atoms.
• Leaving out water in hydrates. CuSO4·5H2O is much heavier than CuSO4.
• Mixing grams and moles. Divide grams by molar mass to get moles.
• Using mass number instead of atomic weight. Carbon is 12.011, not 12, for natural carbon.

Frequently Asked Questions

References & Sources