Molecular Weight Calculator
Calculate approximate molecular weight and molar mass from a chemical formula such as H2O, CO2, or Ca(OH)2.
Status: initial
Results
Awaiting calculation
Molecular Weight Calculator planning panel
Calculate molar mass from a chemical formula with element-level mass details.
Best uses on this page
- Check chemistry homework
- Prepare lab calculations
- Estimate compound molar mass
Check before using results
- Confirm element symbols and parentheses
- Review whether isotope-specific mass is needed
After you calculate
- Compare with molarity inputs
- Copy the element breakdown for notes
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.
When to use this molecular weight calculator
Use it for chemistry homework, lab preparation, and quick molar mass checks for common compounds.
How the calculation works
Molecular weight = sum of each element's atomic weight multiplied by its atom count.
Variable explanations
Enter chemical formula carefully because this value directly affects the result.
Enter element symbol carefully because this value directly affects the result.
Enter atom count carefully because this value directly affects the result.
Enter standard atomic weight carefully because this value directly affects the result.
Formula guide
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.
How to get a better Molecular Weight Calculator result
Calculate molar mass from a chemical formula with element-level mass details.
1. Prepare these inputs
- Chemical formula: Enter a realistic value before calculating.
2. Read these outputs
- Molecular weight: Shown as number.
- Total atoms: Shown as number.
- Element breakdown: Shown as table.
- Result summary: Shown as text.
3. Check the result carefully
- Confirm element symbols and parentheses
- Review whether isotope-specific mass is needed
Compare scenarios one at a time
Find the molecular weight of water
- Enter H2O.
- The calculator counts two hydrogen atoms and one oxygen atom.
- The result is about 18.015 g/mol.
Use the formula as a sanity check
- Molecular Weight Calculator: Molecular weight = sum of each element's atomic weight multiplied by its atom count.
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
Find the molecular weight of water
- Enter H2O.
- The calculator counts two hydrogen atoms and one oxygen atom.
- The result is about 18.015 g/mol.
Common mistakes
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.
FAQs
Is this the same as molar mass?
Does it support hydrates or charged ions?
References
Related calculators
Last updated and version history
Last updated: 2026-08-03
- 1.0.0 (2026-08-03): Initial calculator release with formula tests and SEO-ready content.