Worked example

12.0 g NaCl, M=58.44 → n=0.205 mol.

Moles from Mass

Convert measurable mass to amount of substance.

Equation

$n = \frac{m}{M}$

Inline: $n = \frac{m}{M}$$

Variables

Symbol	Quantity	Unit	Notes
$n$	amount	mol	amount of substance
$m$	mass	g	—
$M$	molar mass	g·mol⁻¹	—

Conditions and limitations

Pure substance; M from sum of atomic weights.

Rearrangements

$m = nM$, $M = m/n$

Dimensional check: g / (g·mol⁻¹)=mol ✓

Worked example

12.0 g NaCl, M=58.44 → n=0.205 mol.

Steps: write equation → substitute with units → check dimensional consistency → report with correct significant figures.

Common errors

• Using atomic number instead of molar mass
• Forgetting to balance before using n

Related resources

• mole-stoichiometry topic
• Calculators — linked only when a real calculator implements this formula.
• Constants — sourced constants with version when values are required.

Sources

• NIST Physical Constants 2022 — CODATA.

Reviewed 2026-08-21 by Editorial Team; due 2027-08-21.