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Molecular Weight Calculator

Calculate approximate molecular weight and molar mass from a chemical formula such as H2O, CO2, or Ca(OH)2.

  • molar mass calculator
  • chemical formula mass calculator
  • molecular mass calculator

Status: initial

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Formula mass and atom count

Explore the molecular weight calculator result visually while keeping this page's detailed guidance and examples.

Formula mass and atom count
Molecular weight180.16 g/mol
Atom count24 atoms

Use this result well

  1. 1Verify the calculator inputs.
  2. 2Compare the key result relationships.
  3. 3Review the page guidance before acting.

Parentheses, hydrates, isotopes, and charge notation require careful formula entry.

Chemistry guide

Molecular Weight Calculator for quick, reliable checks

Calculate approximate molecular weight and molar mass from a chemical formula such as H2O, CO2, or Ca(OH)2. It expands grouped atoms before multiplying each element count by the standard atomic weight stored by the calculator, so the contribution of every supported element remains traceable.

When to use this molecular weight calculator

Use it for chemistry homework, lab preparation, and quick molar mass checks for common compounds. It is best suited to neutral compounds written with conventional element capitalization. Treat the result as an approximate standard molar mass rather than an isotope-specific exact mass.

How the calculation works

Molecular weight = sum of each element's atomic weight multiplied by its atom count. For a formula such as Ca(OH)2, the parentheses multiplier applies to both oxygen and hydrogen before their mass contributions are added to calcium.

Variable explanations

Understand what each input and result means before calculating.

Chemical formula

Enter chemical formula carefully because this value directly affects the result.

Element symbol

Enter element symbol carefully because this value directly affects the result.

Atom count

Enter atom count carefully because this value directly affects the result.

Standard atomic weight

Enter standard atomic weight carefully because this value directly affects the result.

Reviewed by the Calculator.org.in Editorial Team

Formula behavior, validation cases, explanatory examples, and cited sources are checked before publication. This review supports educational accuracy and is not a substitute for qualified professional advice.

Last reviewed: 2026-08-03

Review process

Formula guide

See the calculation logic, variable definitions, and practical meaning.

Molecular Weight Calculator

Molecular weight = sum of each element's atomic weight multiplied by its atom count.

  • Chemical formula
  • Element symbol
  • Atom count
  • Standard atomic weight

The calculator keeps the computation visible through labeled inputs, a primary result, and supporting checks so users can verify the answer before applying it.

Worked examples

Follow realistic inputs through the calculation step by step.

1

Worked example

Find the molecular weight of water

  1. 1Enter H2O.
  2. 2The calculator counts two hydrogen atoms and one oxygen atom.
  3. 3The result is about 18.015 g/mol.
2

Worked example

Calculate carbon dioxide

  1. 1Enter CO2 using an uppercase C and O.
  2. 2Count one carbon atom and two oxygen atoms.
  3. 3Add 12.011 + (2 × 15.999) to obtain about 44.009 g/mol.
3

Worked example

Calculate calcium hydroxide

  1. 1Enter Ca(OH)2.
  2. 2Expand the group to one calcium, two oxygen, and two hydrogen atoms.
  3. 3The approximate molar mass is 74.092 g/mol.

Common mistakes

Avoid these common input and interpretation errors.

Using lowercase element symbols

Review this point before using the result in coursework, planning, purchasing, or documentation.

Forgetting parentheses multipliers

Review this point before using the result in coursework, planning, purchasing, or documentation.

Treating isotope-specific mass as average molar mass

Review this point before using the result in coursework, planning, purchasing, or documentation.

Frequently asked questions

Quick answers to the questions users ask most often.

Is this the same as molar mass?
For everyday chemistry work, molecular weight in g/mol is commonly used as molar mass for a compound.
Does it support hydrates or charged ions?
This version supports standard element symbols and parentheses. Hydrates, charges, and isotope-specific masses should be checked separately.
Why does capitalization matter in a chemical formula?
Element symbols are case-sensitive: Co means cobalt, while CO represents carbon and oxygen. Use the capitalization shown on the periodic table.
Why can published molar masses differ slightly?
Standard atomic weights may be shown with different rounding, and isotope composition can vary. Small differences are normal when sources use different precision.
Can I use the result to convert moles to grams?
Yes. For a supported formula, multiply the amount in moles by the calculated molar mass in grams per mole.

References

Sources used to support the calculator guidance.

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Version history

A transparent record of calculator content updates.

Updated 2026-08-03
  • 1.0.0 · 2026-08-03

    Initial calculator release with formula tests and SEO-ready content.