Skip to content
ENExplore Calculators

Number Of Atoms Calculator

Work out number of atoms instantly with clear inputs, formula shown and shareable results.

About Number Of Atoms Calculator

A mass is turned into an atom count in two steps: divide by the molar mass to get moles, then multiply by the Avogadro constant to get formula units. Multiplying by the atoms in each formula unit finishes the job, so 18 g of water (1 mol) contains 1.81x10^24 atoms rather than 6.02x10^23.

Formulas

Moles from mass

moles = mass / molar mass

Atoms

atoms = moles x 6.022e23 x atoms per formula unit

Worked example

With the default values below, Number Of Atoms Calculator returns Total Atoms of 1.8051 × 10²⁴. Change any input above and every figure here is recalculated in your browser.

Inputs used

Sample massminimum 0 g
18 g
Molar massminimum 0 g/mol
18.015 g/mol
Atoms per formula unitminimum 1
3

Results

Total Atoms
1.8051 × 10²⁴
Moles In Sample
0.999167
Formula Units
6.0171 × 10²³
Atoms Per Gram
1.0029 × 10²³

Step by step

  1. 1Values used
  2. 2Moles from mass
  3. 3Atoms
  4. 4Total Atoms= 1,805,140,000,000,000,000,000,000.0000
  5. 5Moles In Sample= 0.999167
  6. 6Formula Units= 601,713,000,000,000,000,000,000.0000
  7. 7Atoms Per Gram= 100,285,000,000,000,000,000,000.0000

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Does this need the substance to be pure?

Yes. The molar mass entered is assumed to describe the whole sample, so for a mixture you would work out each component separately.

What if I only want molecules, not atoms?

Set atoms per formula unit to 1 and the atom total becomes the formula-unit total.

Related Calculators

Number Of Atoms Calculator | Calcrivo