Moles to Grams Calculator

Convert between moles, grams and number of particles for any chemical formula.

Substance

Try:

Mass

Mass: 25 g
Moles: 1.3877 mol
Particles: 8.357 × 10^23
Volume at STP (gas): 31.5168 L

Working

M = 18.015 g/mol
n = m ÷ M = 25 g ÷ 18.015 g/mol = 1.38773 mol
Nᴀ = 6.02214076 × 10²³ per mole (exact, by definition)

The mole map

Almost every quantitative chemistry problem is a walk across the same three-point map: grams, moles, particles. Moles sit in the middle, and you can never go directly from grams to particles without passing through them. Molar mass is the bridge on one side, Avogadro’s number on the other.

Why the mole exists

Atoms are far too light to weigh individually, but reactions happen atom by atom. The mole reconciles the two: it is the number of particles that makes a formula’s mass in grams come out as a convenient laboratory quantity, so a balanced equation written in molecules can be carried out on a balance.

How it works

Almost every quantitative chemistry problem is a walk across the same three-point map: grams, moles, particles. Moles sit in the middle, and you cannot go from grams to particles without passing through them.

Mole conversions

n = m ÷ M          m = n × M

N = n × Nᴀ        n = N ÷ Nᴀ

Nᴀ = 6.02214076 × 10²³ mol⁻¹  (exact, by definition)

n: amount of substance, in moles
m: mass, in grams
M: molar mass, g/mol
N: number of particles
Nᴀ: Avogadro's number

25 g of water

m = 25 g
M(H₂O) = 18.015 g/mol

n = 25 ÷ 18.015 = 1.388 mol
N = 1.388 × 6.022 × 10²³

1.388 mol, or 8.36 × 10²³ water molecules — and about 2.5 × 10²⁴ atoms, since each molecule has three.

Good to know

Since 2019 the mole is DEFINED as exactly 6.02214076 × 10²³ entities, so Avogadro’s number has no uncertainty.
A mole of water contains that many molecules but three times as many atoms. Be clear which you are counting.
One mole of an ideal gas occupies 22.71 L at STP (0 °C, 100 kPa) or 24.79 L at 25 °C. That applies to gases only.
Molar mass is the bridge on the mass side and Avogadro’s number the bridge on the particle side — there is no direct route between grams and particles.

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Frequently Asked Questions

How do you convert moles to grams?

Multiply the number of moles by the molar mass: m = n × M. Two moles of carbon dioxide, molar mass 44.01 g/mol, weigh 88.02 g.

How do you convert grams to moles?

Divide the mass by the molar mass: n = m ÷ M. 25 g of water divided by 18.015 g/mol gives 1.388 mol.

What is a mole?

A mole is a counting unit, like a dozen but far larger: exactly 6.02214076 × 10²³ particles. Since 2019 that number is the definition rather than something measured, which is why it has no uncertainty.

How many particles are in a mole?

6.02214076 × 10²³ — Avogadro’s number. Multiply moles by it to get particles, divide to go back. Note that a mole of water contains that many molecules, but three times as many atoms.

What volume does a mole of gas occupy?

22.71 L at STP (0 °C and 100 kPa) for an ideal gas, or 24.79 L at 25 °C. That only applies to gases, and only approximately to real ones — for anything precise, use the ideal gas law.