Mole Formula Explained

This reference explains the Mole formula used by our free Mole Calculator. Use it to understand variables, units, and common mistakes before you calculate.

The formula

n = mass (g) ÷ molar mass (g/mol); N = n × N_A

Variables and units

• n — Amount of substance (mol)
• m — Mass (g)
• M — Molar mass (g/mol)
• N_A — Avogadro's number (6.022 × 10²³ mol⁻¹)

Worked example

Inputs: Calculate moles in 36 g of water (H₂O, M = 18 g/mol)

1. n = m / M = 36 / 18 = 2 mol
2. Particles = 2 × 6.022 × 10²³ = 1.204 × 10²⁴ molecules

Result: 2 moles of water = 1.204 × 10²⁴ molecules

When to use this formula

Use this formula when you need a quick mole estimate with values you already know. Our Mole Calculator applies the same relationship automatically so you can verify handwritten work.

Common mistakes

• Using molecular weight in kg/mol without converting mass to kg
• Confusing molar mass with molecular weight units
• Forgetting to balance equations before mole ratios

Frequently asked questions