Molar Mass Calculator

Molar mass is the mass of one mole of a substance in grams. It equals the sum of atomic masses of all atoms in the formula. Used to convert between mass and moles in every chemistry calculation.

⚗️ Stoichiometry📐 M = ∑(Aᵢ × nᵢ)🧪 General Chemistry
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Formula & Reference

VariableSymbolFormulaUnits
Molar MassM∑(atomic mass × count)g/mol
Moles from Massnn = m/Mmol
Mass from Molesmm = n × Mg
Common: H1.008H2O: 2(1.008)+16.00 = 18.02g/mol
Common: C12.011CO2: 12.011+2(16.00) = 44.01g/mol

Step-by-Step Examples

Example 1
Water H₂O

Find molar mass of water.

  • H: 2 × 1.008 = 2.016 g/mol
  • O: 1 × 16.00 = 16.00 g/mol
  • Total: 18.016 g/mol
✓ M(H₂O) = 18.02 g/mol
Example 2
Glucose C₆H₁₂O₆

Find molar mass of glucose.

  • C: 6 × 12.011 = 72.066
  • H: 12 × 1.008 = 12.096
  • O: 6 × 15.999 = 95.994
  • Total = 180.156 g/mol
✓ M(C₆H₁₂O₆) = 180.16 g/mol
Example 3
Sulfuric Acid H₂SO₄

Find molar mass of H₂SO₄.

  • H: 2×1.008=2.016
  • S: 1×32.065=32.065
  • O: 4×15.999=63.996
  • Total=98.077 g/mol
✓ M(H₂SO₄) = 98.08 g/mol

Real-World Applications

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Laboratory Calculations
Every gram-to-mole conversion in lab work requires molar mass. Foundation of quantitative chemistry.
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Pharmaceutical Dosing
Drug doses are calculated by moles; molar mass converts to practical gram quantities.
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Industrial Chemistry
Chemical plants calculate reactant quantities using molar mass for stoichiometric ratios.
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Analytical Chemistry
Gravimetric analysis converts measured masses to moles using molar mass.

Common Mistakes to Avoid

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Counting all atoms carefully

Subscripts apply to the atom immediately before. H₂SO₄: 2 H, 1 S, 4 O. Parentheses: Ca(OH)₂ has 1 Ca, 2 O, 2 H.

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Using outdated atomic masses

Use IUPAC 2021 values: H=1.008, C=12.011, O=15.999, N=14.007, S=32.065, Cl=35.453.

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Confusing molar mass with molecular mass

Molar mass (g/mol) and molecular mass (amu) are numerically equal but different units. Molar mass applies to bulk amounts.

Frequently Asked Questions

What is the difference between molar mass and molecular weight? ▾
They are numerically the same but different conceptually. Molecular weight (amu) refers to one molecule. Molar mass (g/mol) refers to one mole of molecules. The numbers are equal by Avogadro definition.
How do I find molar mass of ionic compounds? ▾
Same method: sum atomic masses of all ions. NaCl: 22.990 + 35.453 = 58.443 g/mol. No need to consider charges for molar mass calculation.
What is the molar mass of air? ▾
Air is ~78% N₂ (28.014) + 21% O₂ (31.998) + 1% Ar (39.948). Weighted average: ~28.97 g/mol.
How does molar mass relate to the mole? ▾
1 mole = 6.022×10²³ particles. Molar mass tells you: 1 mole of this substance has this many grams. e.g., 1 mol H₂O = 18.02 g = 6.022×10²³ molecules.
Why is carbon-12 important for molar mass? ▾
The mole is defined so that 12 g of carbon-12 contains exactly 6.022×10²³ atoms. This ties atomic mass units to grams per mole.

Related Chemistry Calculators

⚗️ Grams to Moles⚗️ Moles to Grams🧪 Molarity📊 Percent Composition⚖️ Stoichiometry

Formula Explorer connections

Interpretation: This relationship converts chemical amount, mass, composition or balanced-equation ratios into a reaction quantity. Assumption: Use a balanced reaction, consistent units and the correct molar mass. Purity, side reactions and limiting reagents can change experimental results.

Molar Mass Reference Calculator →Molecular Formula Calculator →Moles Calculator →Chemistry Formula Explorer →