Chemistry

Grams to Moles Calculator

Convert grams to moles using molecular weight. Essential for chemistry calculations and stoichiometry.

Calculation mode
g
Molar mass: 18.015 g/mol
Moles
5.550930
Mass
100 g
Molar mass
18.015 g/mol
Moles
5.550930
Molecules
3.343 × 10^24

Avogadro's number: 6.022 × 10²³ molecules/mol

Grams to moles conversion

Converting between grams and moles is fundamental in chemistry. The mole is the SI unit for amount of substance.

Formula

Moles=Mass (g)Molecular Weight (g/mol)\text{Moles} = \frac{\text{Mass (g)}}{\text{Molecular Weight (g/mol)}}

What is a mole?

A mole is a unit that represents 6.022 × 10²³ particles (Avogadro's number). This number of particles of any substance has a mass equal to its molecular weight in grams.

Common molecular weights

CompoundFormulaMolecular Weight
WaterH₂O18.015 g/mol
Sodium chlorideNaCl58.44 g/mol
Carbon dioxideCO₂44.01 g/mol
GlucoseC₆H₁₂O₆180.16 g/mol
Sulfuric acidH₂SO₄98.079 g/mol

Calculating molecular weight

Add the atomic masses of all atoms in the molecule:

Example: Water (H₂O)

MW=2×H+1×O=2×1.008+1×15.999=18.015 g/mol\begin{aligned} \text{MW} &= 2 \times \text{H} + 1 \times \text{O} \\ &= 2 \times 1.008 + 1 \times 15.999 \\ &= 18.015 \text{ g/mol} \end{aligned}

Example calculation

How many moles are in 100g of water?

Moles=100 g18.015 g/mol=5.55 mol\begin{aligned} \text{Moles} &= \frac{100 \text{ g}}{18.015 \text{ g/mol}} \\ &= 5.55 \text{ mol} \end{aligned}

Why moles matter

  • Stoichiometry: Chemical equations work with moles, not grams
  • Solutions: Molarity is moles per liter
  • Reactions: Products and reactants relate by mole ratios
  • Gas laws: Ideal gas law uses moles