What is the difference between molecular weight and molar mass?

They are numerically the same value here. Molecular weight is a relative, unitless figure, while molar mass carries the unit grams per mole (g/mol); this calculator reports the number you can use directly as molar mass.

How should I write the chemical formula?

Use proper element symbols with an uppercase first letter and optional lowercase second letter, followed by a count for multiple atoms (for example H2O or CaCl2). Capitalisation is significant, so Co means cobalt while Co with a separate O is read differently.

Does this calculator handle parentheses or hydrates?

No. The parser reads a flat sequence of element symbols and counts, so expand groups yourself — write Ca(OH)2 as CaO2H2 — and it does not interpret dot notation for hydrates.

Why does my formula return an "unknown element" error?

The symbol you entered is not in the periodic table data, usually because of a typo or wrong capitalisation. Check that each element symbol is spelled and capitalised correctly.

Molecular Weight Calculator

Chemical Formula

Molecular Weight18.015 g/mol

H x22.016 g/mol

O x115.999 g/mol

This molecular weight calculator parses a chemical formula and adds up the atomic weights of every atom it contains to give the molar mass in grams per mole. Type a formula such as H2O or C6H12O6 and it returns the total weight plus a per-element breakdown. It is a quick aid for stoichiometry, solution preparation, and lab bench calculations.

Formula

MW = Σ (atomic_weight × count)

MW: Molecular weight (molar mass) in grams per mole (g/mol)
atomic_weight: Standard atomic weight of each element from the periodic table
count: Number of atoms of that element in the formula (subscript)

How it works

Enter a chemical formula using element symbols and counts, for example NaCl or C6H12O6 (capitalisation matters: Co is cobalt, CO is carbon plus oxygen).
The parser reads each element symbol and its subscript, treating a missing subscript as one atom.
Each element's standard atomic weight is multiplied by its count, and all contributions are summed to give the total molar mass in g/mol.

Worked example

Find the molecular weight of glucose, C6H12O6.

Carbon: 6 × 12.011 = 72.066.
Hydrogen: 12 × 1.008 = 12.096.
Oxygen: 6 × 15.999 = 95.994.
Sum: 72.066 + 12.096 + 95.994 = 180.156.

Molecular weight of C6H12O6 ≈ 180.156 g/mol.

Frequently asked questions

What is the difference between molecular weight and molar mass?: They are numerically the same value here. Molecular weight is a relative, unitless figure, while molar mass carries the unit grams per mole (g/mol); this calculator reports the number you can use directly as molar mass.
How should I write the chemical formula?: Use proper element symbols with an uppercase first letter and optional lowercase second letter, followed by a count for multiple atoms (for example H2O or CaCl2). Capitalisation is significant, so Co means cobalt while Co with a separate O is read differently.
Does this calculator handle parentheses or hydrates?: No. The parser reads a flat sequence of element symbols and counts, so expand groups yourself — write Ca(OH)2 as CaO2H2 — and it does not interpret dot notation for hydrates.
Why does my formula return an "unknown element" error?: The symbol you entered is not in the periodic table data, usually because of a typo or wrong capitalisation. Check that each element symbol is spelled and capitalised correctly.

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