Molecular Weight Calculator
Calculate molecular weight from a chemical formula and see every element's atom count, atomic weight, mass contribution, and percentage of the total.
- molar mass calculator
- chemical formula mass calculator
- molecular mass calculator
Use case-sensitive element symbols and whole-number subscripts, such as H2O, C6H12O6, or Ca(OH)2.
Status: initial
Results
Awaiting calculation
From chemical formula to molecular weight
The calculator identifies each element, applies its subscript or parentheses multiplier, and shows how every contribution builds the total.
Try a valid example
Element contribution by mass
- Step 1Parse the formula
Read element symbols, subscripts, and parentheses multipliers.
- Step 2Calculate each element
Multiply every atom count by that element's standard atomic weight.
- Step 3Add contributions
Sum the element contributions to obtain the molecular weight.
Atomic weights are abridged standard values for normal materials. Radioactive elements without a standard atomic weight require an isotope-specific calculation.
Molecular Weight Calculator for quick, reliable checks
Calculate molecular weight from a chemical formula and see every element's atom count, atomic weight, mass contribution, and percentage of the total. 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, solution preparation, stoichiometry, and quick molar-mass checks. The result explains how much each element contributes instead of presenting only a final number. 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
For each element, mass contribution = atom count × standard atomic weight. Molecular weight = sum of all element contributions. 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.
Mass contribution
Enter mass contribution 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: 2026-08-23
Formula guide
See the calculation logic, variable definitions, and practical meaning.
Molecular Weight Calculator
For each element, mass contribution = atom count × standard atomic weight. Molecular weight = sum of all element contributions.
- Chemical formula
- Element symbol
- Atom count
- Standard atomic weight
- Mass contribution
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.
Worked example
Find the molecular weight of water
- 1Enter H2O.
- 2Hydrogen contributes 2 × 1.008 = 2.016 g/mol.
- 3Oxygen contributes 1 × 15.999 = 15.999 g/mol, for a total of 18.015 g/mol.
Worked example
Calculate carbon dioxide
- 1Enter CO2 using an uppercase C and O.
- 2Count one carbon atom and two oxygen atoms.
- 3Add 12.011 + (2 × 15.999) to obtain about 44.009 g/mol.
Worked example
Calculate calcium hydroxide
- 1Enter Ca(OH)2.
- 2Expand the group to one calcium, two oxygen, and two hydrogen atoms.
- 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.
Starting a formula with a coefficient instead of entering one molecule
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?
Does it support hydrates or charged ions?
Why does the element table show a percentage?
Why does capitalization matter in a chemical formula?
Why can published molar masses differ slightly?
Can I use the result to convert moles to grams?
References
Sources used to support the calculator guidance.
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Version history
A transparent record of calculator content updates.
- 1.1.0 · 2026-08-23
Added field-level formula validation, broader element coverage, and a complete element-by-element mass calculation table.
- 1.0.0 · 2026-08-03
Initial calculator release with formula tests and SEO-ready content.