Molecular Weight Calculator

Last updated: June 2026

Chemical formula

Molar mass

18.015 g/mol

Element breakdown

Element	Count	Atomic mass	Total
H	2	1.008	2.016
O	1	15.999	15.999

Formula

Molar mass = sum of each element count x atomic mass. Brackets are multiplied by the number after the closing bracket, for example Ca(OH)2 has two O atoms and two H atoms.

Common compounds

Compound	Molar mass
Water H2O	18.015 g/mol
NaCl	58.443 g/mol
CO2	44.010 g/mol
Glucose C6H12O6	180.156 g/mol
Ethanol C2H5OH	46.068 g/mol

About this calculator

The Molecular Weight Calculator estimates molar mass from a chemical formula. It is useful for stoichiometry, molarity questions, preparing solutions, and checking formula masses for common compounds such as water, sodium chloride, carbon dioxide, and glucose.

Molar mass method

The calculator parses the chemical formula into element counts, multiplies each count by atomic mass, and sums the totals.

molar mass = sum(element count x atomic mass)
Ca(OH)2 = Ca x 1 + O x 2 + H x 2

How to use the molecular weight calculator

Enter a chemical formula such as H2O, NaCl, C6H12O6, or Ca(OH)2.
Use correct capitalisation for element symbols.
Put bracketed groups in parentheses where needed.
Check the element breakdown table.
Review each element count and contribution.
Use the total molar mass in grams per mole for later calculations.

Worked examples

Water

Input: H2O

Calculation: 2 x H plus 1 x O = 2 x 1.008 + 15.999

Result: 18.015 g/mol

Calcium hydroxide

Input: Ca(OH)2

Calculation: Ca x 1, O x 2, H x 2

Result: About 74.092 g/mol

Formula parsing rules

Element symbols are case-sensitive. CO means carbon monoxide, while Co would mean cobalt if cobalt were included in the atomic mass table.

Common compounds

Compound	Molar mass
H2O	18.015 g/mol
NaCl	58.443 g/mol
CO2	44.010 g/mol
C6H12O6	180.156 g/mol

Atomic mass table limitation

This calculator includes a focused atomic mass table for common school and early college chemistry. Very uncommon elements, isotopic masses, hydrates, and charged species may need specialist data.

Frequently asked questions

Is molecular weight the same as molar mass?

In many classroom contexts they are used similarly, although molar mass is usually expressed in g/mol.

Does the calculator handle brackets?

Yes, simple bracketed groups such as Ca(OH)2 are supported.

Why does capitalisation matter?

Element symbols use capitalisation to distinguish elements.

Can it calculate hydrates?

Hydrates are not fully modelled unless entered as an expanded formula.

Can I use the result for molarity?

Yes, molar mass can convert grams to moles before a molarity calculation.

Related calculators

molarity-calculator
concentration-calculator
scientific-calculator

What does this mean?

This calculator is designed to help you understand the likely number before you make a decision or start an application.

Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.

Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.