Convert grams to moles and moles to grams using molar mass. Enter mass and molar mass for instant chemistry calculations. Essential for stoichiometry and lab work.
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Find in periodic table: sum of atomic masses of all atoms
Convert grams to moles and moles to grams using molar mass. Enter mass and molar mass for instant chemistry calculations. Essential for stoichiometry and lab work.
Moles
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⚠️ Disclaimer: Verify molar masses against current IUPAC atomic weights before use in research or professional lab work. Atomic masses are periodically updated as measurement precision improves.
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Sources & Methodology
✓Formulas verified against authoritative sources listed below.
National Institute of Standards and Technology chemical data including molar masses
Methodology: Moles = Mass (g) / Molar Mass (g/mol). Number of molecules = Moles x Avogadro's number (6.022 x 10^23). Molar mass = sum of atomic masses from periodic table for each atom in the formula.
⏱ Last reviewed: April 2026
How to Convert Grams to Moles
The mole is the fundamental unit of amount of substance in chemistry. Converting between grams (mass) and moles (amount) is one of the most common calculations in chemistry, required for stoichiometry, solution preparation, reaction yield calculations, and lab work. The conversion uses the molar mass as a bridge between mass and amount.
The Grams to Moles Formula
Moles = Mass (grams) ÷ Molar Mass (g/mol). For example, water (H₂O) has a molar mass of 18.015 g/mol. To find moles in 36 g of water: 36 ÷ 18.015 = 1.998 mol ≈ 2 mol. This means 36 grams of water contains approximately 2 moles of water molecules.
What is Molar Mass?
Molar mass is the mass in grams of one mole of a substance, equal to the sum of atomic masses of all atoms in the formula. For H₂O: 2(1.008) + 15.999 = 18.015 g/mol. For NaCl: 22.990 + 35.453 = 58.443 g/mol. Find atomic masses on the periodic table.
Avogadro's Number and the Mole
One mole contains exactly 6.02214076 × 10²³ particles (Avogadro's number). This is not arbitrary — it is defined so that one mole of carbon-12 atoms has a mass of exactly 12 grams. This connects the macroscopic (grams) to the atomic scale (individual atoms and molecules).
Converting Moles Back to Grams
To convert moles to grams: Mass (g) = Moles × Molar Mass (g/mol). For 3.5 moles of NaCl (58.443 g/mol): Mass = 3.5 × 58.443 = 204.55 g. This reverse conversion is used when you know how many moles of reactant or product you need and want to weigh out the correct amount.
Grams to Moles Formula
Moles = Mass (g) ÷ Molar Mass (g/mol) | Molecules = Moles × 6.022 × 10²³
Molar mass = sum of atomic masses from periodic table. Avogadro's number = 6.02214076 × 10²³ mol⁻¹. Both formulas are exact by definition under the 2019 SI redefinition.
Substance
Formula
Molar Mass (g/mol)
Water
H₂O
18.015
Carbon dioxide
CO₂
44.009
Sodium chloride
NaCl
58.443
Glucose
C₆H₁₂O₆
180.156
Sulfuric acid
H₂SO₄
98.072
Calcium carbonate
CaCO₃
100.086
Ethanol
C₂H₅OH
46.068
Ammonia
NH₃
17.031
💡 Chemistry Tip: When calculating molar mass from a formula, count ALL atoms in the formula including subscript numbers. For Ca(OH)₂: 1 Ca (40.078) + 2 O (2 × 15.999) + 2 H (2 × 1.008) = 74.092 g/mol. Parentheses multiply everything inside by the subscript outside.
Frequently Asked Questions
Divide mass in grams by the molar mass in g/mol: Moles = Mass / Molar Mass. For 54 g of water (molar mass 18.015 g/mol): Moles = 54 / 18.015 = 2.998 mol ≈ 3 mol.
Moles = Mass (g) / Molar Mass (g/mol). This is the fundamental mole conversion formula. To convert back: Mass (g) = Moles × Molar Mass (g/mol).
Add up the atomic masses of all atoms in the chemical formula. Find atomic masses on the periodic table. For H₂SO₄: 2(1.008) + 32.065 + 4(15.999) = 2.016 + 32.065 + 63.996 = 98.077 g/mol.
Exactly 6.02214076 × 10²³ molecules (Avogadro's number). This number was chosen so that one mole of carbon-12 has a mass of exactly 12 grams.
Multiply moles by molar mass: Mass (g) = Moles × Molar Mass (g/mol). For 2.5 mol of NaCl (58.443 g/mol): Mass = 2.5 × 58.443 = 146.11 g.
Water (H₂O) has a molar mass of 18.015 g/mol: 2 × hydrogen (1.008) + 1 × oxygen (15.999) = 2.016 + 15.999 = 18.015 g/mol.
Moles allow chemists to work with the exact proportions of atoms and molecules specified in chemical equations, without needing to count individual atoms. A chemical equation like H₂ + ½O₂ → H₂O means 1 mole of hydrogen reacts with 0.5 moles of oxygen to produce 1 mole of water.
Sodium chloride (NaCl) has a molar mass of 58.443 g/mol: Na (22.990 g/mol) + Cl (35.453 g/mol) = 58.443 g/mol.
100 g ÷ 18.015 g/mol = 5.551 moles of water. This contains 5.551 × 6.022 × 10²³ = 3.342 × 10²⁴ molecules.
Moles is a quantity (amount of substance). Molarity is moles per liter of solution (mol/L or M). A 1M solution of NaCl contains 1 mole of NaCl dissolved per liter of solution. Moles describes how much; molarity describes concentration.