Molecular Weight Calculator
Enter a chemical formula (e.g. H2O, NaCl, C6H12O6, Ca(OH)2) to calculate its molecular weight in grams per mole.
Last updated: September 26, 2026
Frequently asked questions
How do I calculate the molecular weight of water (H2O)?
Add up the atomic weights: 2 hydrogen atoms (2 × 1.008 = 2.016) plus 1 oxygen atom (15.999), for a total of about 18.015 g/mol.
What's the difference between molecular weight and molar mass?
They're the same value expressed differently - molecular weight is technically a dimensionless ratio, while molar mass carries units (grams per mole, g/mol), but in practice the numbers are identical and the terms are used interchangeably.
How do I enter a formula with parentheses, like Ca(OH)2?
Type it exactly as written - this calculator supports parentheses with a multiplier, so Ca(OH)2 correctly counts 1 calcium, 2 oxygen, and 2 hydrogen atoms (the 2 outside the parentheses multiplies everything inside).
Is a 'molecular weight calculators' or 'calculate molecular weights' search different from this tool?
No - plural, verb, and noun forms of the same phrase all point to the same task: entering a chemical formula and getting its total molar mass back, which is exactly what this calculator does.
Is 'molar weight calculator' or 'mol wt calculator' the same as molecular weight?
Yes - "molar weight," "mol wt," "molecular weight," and "molar mass" are all names for the same quantity: the mass of one mole of a substance, in grams per mole. This calculator computes it from any chemical formula you enter.
How do we calculate molar mass?
Add up the atomic weight of each element in the formula, multiplied by how many atoms of that element appear - for H2O, that's 2 × 1.008 (hydrogen) + 1 × 15.999 (oxygen) = 18.015 g/mol. Enter any formula above and this calculator does that sum for you.