Molecular Weight Calculator

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Pick a preset to auto-fill the formula, or choose "Enter formula below" to type your own.
Type the molecular formula using element symbols. Use numbers for subscripts (H2O, not H₂O). Parentheses for groups: Al2(SO4)3. Hydrates: CuSO4*5H2O or CuSO4.5H2O.
Optional: enter the number of moles to calculate the mass of that sample.
mol
Molar mass
18.016g/mol

Mass of one mole of the compound (numerically equal to molecular weight in Da)

Mass of sample18.016g
Atoms per molecule3
Number of elements2
Elemental compositionH: 2 atoms, 2.016 g/mol (11.19%) | O: 1 atom, 16.000 g/mol (88.81%)
Total atoms3
Distinct elements2

Molar mass of H2O: 18.0160 g/mol

  • O makes up the largest share of the mass at 88.8% by weight.
  • Each formula unit contains 3 atoms across 2 elements.
  • This is a light molecule: one mole weighs less than 50 g, comparable to a small bottle of water.

Next stepUse the molar mass with Avogadro's number (6.022 × 10²³ mol⁻¹) to convert between moles and the number of individual molecules.

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