Grams ⇄ Moles ⇄ Particles Converter

Understanding the grams to moles converter — concept and principle

Chemists weigh substances in grams but reactions happen particle by particle. This converter takes a chemical formula and a mass and gives the amount in moles, the number of particles (molecules or formula units) and the molar mass it used. It is the first step in stoichiometry, preparing solutions and checking reaction yields.

Divide grams by the molar mass to get moles, then multiply by Avogadro’s number to count the particles.

How it is calculated

n = m ÷ M: moles n (mol) equal the mass m (g) divided by the molar mass M (g/mol).
N = n × N_A: the number of particles N equals moles times the Avogadro constant N_A = 6.02214076 × 10²³ mol⁻¹.
M is computed from the formula by summing standard atomic weights, so parentheses and hydrates are handled automatically.

The principle

The mole is a counting unit, like a dozen, only much larger: one mole is exactly 6.02214076 × 10²³ entities by the 2019 SI definition. Molar mass tells you how many grams one such batch weighs. Dividing the mass by the mass of one batch gives the number of batches, and multiplying by the batch size gives the number of particles. For an ionic solid such as NaCl the "particle" is one formula unit (one Na⁺ plus one Cl⁻), not a molecule.

Worked example

Defaults: formula NaCl, mass 58.44 g.

Molar mass: 22.990 (Na) + 35.45 (Cl) = 58.44 g/mol.
Moles: 58.44 ÷ 58.44 = 1 mol.
Particles: 1 × 6.02214076 × 10²³ = 6.022141 × 10²³ formula units.

Each point is the calculator re-run with only “Mass (g)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Mass (g)	Moles
14.6	0.25
29.2	0.5
43.8	0.75
58.4	1
73	1.25
87.7	1.5
117	2

How to read the result

One mole of any substance contains the same number of particles, but the masses differ: 1 mol of NaCl is 58.44 g, 1 mol of water about 18.02 g. When you compare amounts in a reaction, compare moles, not grams. Particle counts are useful for intuition and in physics or nanotechnology; for lab work moles are the practical unit.

Common mistakes

Dividing the molar mass by the mass instead of the mass by the molar mass.
Counting ions as separate particles when the question asks for formula units (1 mol NaCl gives 2 mol of ions when dissolved).
Using a mass in milligrams or kilograms without converting to grams.
Forgetting water of crystallisation in a hydrated reagent, which changes M.

Keep in mind: The result assumes a pure substance. Real reagents have a purity (for example 99.5%) and may absorb moisture, so correct the mass for purity before calculating for accurate work.

Frequently asked questions

How many molecules are in 1 gram of water?

Water is about 18.015 g/mol, so 1 g is 0.0555 mol, or about 3.34 × 10²² molecules.

How do I convert moles back to grams?

Multiply moles by molar mass: m = n × M.

Is the Avogadro constant exact?

Yes. Since the 2019 SI redefinition it is fixed at exactly 6.02214076 × 10²³ mol⁻¹.

Sources: BIPM, The International System of Units (SI Brochure), 9th edition, 2019 · IUPAC Commission on Isotopic Abundances and Atomic Weights, Standard atomic weights

Checked 8 Nov 2026. Standard textbook formulas in SI units, computed in your browser. For learning and estimates — real designs must follow your local codes and be checked by a qualified engineer.

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