Calculate Moles, Mass, or Molar Mass | n = m / M | Chemistry Tool
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📝 Step-by-step solution
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💡 Moles n in mol | Mass m in grams (g) | Molar Mass M in g/mol | 1 mol = 6.022 × 10²³ particles
📖 What is a Mole?
A mole (mol) is the SI unit for the amount of substance.
One mole contains exactly 6.022 × 10²³ particles (Avogadro's number) —
whether those particles are atoms, molecules, ions, or electrons.
The mole bridges the gap between the microscopic world of atoms and the macroscopic world we can measure.
This calculator uses the fundamental relationship between mass, moles, and molar mass:
n = m / M
Where:
• n = Number of moles (mol)
• m = Mass of substance (g)
• M = Molar mass (g/mol)
🔁 Rearranged Formulas
Moles: n = m / M Mass: m = n × M Molar Mass: M = m / n
📝 Worked Example
Example: How many moles are in 36 g of water (H₂O)?
Given: Mass m = 36 g | Molar mass of H₂O = 18.015 g/mol
Step 1: Molar mass of H₂O = 2 × 1.008 (H) + 15.999 (O) = 18.015 g/mol Step 2: n = m / M = 36 / 18.015 Step 3: n ≈ 1.998 mol ≈ 2 moles
Result: 36 g of water contains approximately 2 moles of H₂O molecules.
⚛️ Avogadro's Number
1 mole = 6.02214076 × 10²³ particles
This means 1 mole of any substance contains the same number of particles.
For example:
1 mole of H₂O = 6.022 × 10²³ water molecules
1 mole of carbon = 6.022 × 10²³ carbon atoms
1 mole of NaCl = 6.022 × 10²³ NaCl formula units
📊 Common Molar Masses
Hydrogen (H): 1.008 g/mol
Carbon (C): 12.011 g/mol
Nitrogen (N): 14.007 g/mol
Oxygen (O): 15.999 g/mol
Water (H₂O): 18.015 g/mol
Carbon dioxide (CO₂): 44.01 g/mol
Sodium chloride (NaCl): 58.44 g/mol
Glucose (C₆H₁₂O₆): 180.16 g/mol
⚠️ Limitations & Assumptions
📌 Important Notes
Assumes you know the correct molar mass for the substance.
Results assume 100% pure substance — real samples may have impurities.
Does not account for hydrates unless water mass is included in molar mass.
Uses standard atomic weights — isotopic variations are not considered.
Molar mass must be in g/mol and mass in grams for consistency.
Results are theoretical — experimental values may differ slightly.
📚 Sources & References
Authoritative Sources
IUPAC — Atomic Weights of the Elements
NIST — SI Units and Avogadro Constant
OpenStax — Chemistry 2e, Chapter 3: Composition of Substances and Solutions
Khan Academy — The Mole and Avogadro's Number
CRC Handbook of Chemistry and Physics
❓ Frequently Asked Questions
What is a mole in chemistry?
A mole is the SI unit for amount of substance. It represents 6.022 × 10²³ particles
(atoms, molecules, ions, etc.) — a number known as Avogadro's number.
How do I find the molar mass of a compound?
Add up the atomic masses of all atoms in the formula. For example, H₂O = 2 × 1.008 + 15.999 = 18.015 g/mol.
Use a periodic table for accurate atomic masses.
What is the difference between molar mass and molecular mass?
Molecular mass is the mass of one molecule in atomic mass units (u or Da).
Molar mass is the mass of one mole of a substance in grams (g/mol).
Numerically, they are the same value.
Can I calculate moles from volume of a gas?
Yes — at standard temperature and pressure (STP), 1 mole of any ideal gas occupies 22.4 L.
Use: n = V / 22.4 (at STP). Use our Ideal Gas Law calculator for other conditions.
Why is the mole important?
The mole lets chemists count atoms and molecules by weighing them.
It is essential for stoichiometry, reaction calculations, solution preparation, and lab work.
This Mole Calculator is provided for informational and educational purposes only.
Results are based on standard chemistry formulas and assumed molar masses.
Real-world values may vary due to impurities, isotopic composition, temperature, and measurement uncertainty.
Always verify critical calculations with authoritative sources (IUPAC, NIST) or a qualified chemistry professional.