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⚗️ Molecular Weight Calculator

Enter any chemical formula to find its molar mass, with a full element-by-element breakdown.

⚗️ Chemical Formula
H₂O
C₆H₁₂O₆
NaCl
Ca(OH)₂
Al₂(SO₄)₃
C₁₂H₂₂O₁₁
📊 Molar Mass
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⚗️

Enter a chemical formula and click Calculate

Guide

About the Molecular Weight Calculator

Last updated: July 2026 · Reviewed by the NeftCal editorial team

This free molecular weight calculator parses any chemical formula — from something as simple as H₂O to a complex formula with nested parentheses like Al₂(SO₄)₃ — and instantly computes its molar mass, with a full element-by-element breakdown showing exactly how each atom's contribution adds up.

How It Works

Type a chemical formula using standard notation, and the calculator parses it character by character: identifying element symbols (one capital letter, optionally followed by a lowercase letter), reading any subscript numbers that follow, and correctly expanding parentheses groups by multiplying everything inside by the subscript that follows the closing parenthesis. Each element's count is then multiplied by its standard atomic weight from a built-in periodic table, and all the contributions are summed into the final molar mass in grams per mole.

Who Should Use This Calculator

Chemistry students calculating molar mass for stoichiometry and molarity problems, lab technicians preparing solutions who need a compound's molar mass, and anyone curious about the composition of a chemical formula. It's a formula-parsing calculation tool, not a chemical database — always verify unusual or hydrate formulas against a reliable reference.

Real-World Applications

  • Finding a compound's molar mass for stoichiometry and molarity calculations
  • Checking chemistry homework answers involving molecular weight
  • Preparing lab solutions that require a precise molar mass figure
  • Comparing the molar mass of related compounds (e.g. different hydrates or salts)
  • Pairing with NeftCal's Molarity Calculator to go from formula straight to solution concentration

Tips for Accurate Results

  • Use correct capitalization — one capital letter starts every element symbol, with at most one lowercase letter following (Co is cobalt; CO is carbon monoxide).
  • Wrap repeated groups in parentheses with a trailing number, like (NH4)2SO4, rather than typing atoms out individually.
  • Double-check subscript numbers carefully — a missing or extra digit changes the entire result.
  • For hydrated compounds (like CuSO4·5H2O), calculate the anhydrous formula and the water separately, then add the two molar masses together.
Formula

How Molecular Weight Is Calculated

The parsing and summation logic this calculator uses

Per-Element Contribution
Element Mass = Atomic Weight × Number of Atoms in the Formula

Total Molecular Weight
Molecular Weight = Σ (Element Mass) for every element in the formula

Parentheses Groups
Group Contribution = (Sum of atoms inside the parentheses) × Subscript After the Closing Parenthesis
🔤

Element Symbol Parsing

Every element symbol starts with exactly one capital letter, optionally followed by one lowercase letter — the calculator reads formulas the same way a chemist does.

🔢

Subscript Multipliers

A number immediately following an element or a closing parenthesis multiplies that element's (or group's) atom count; no number means a count of exactly 1.

🔗

Nested Parentheses

Groups in parentheses, like (SO4) in Al2(SO4)3, are resolved first and then scaled by their trailing subscript before being merged into the total atom count.

⚙️ Why This Approach Works

Chemical formula notation follows strict, unambiguous rules — capitalization marks element boundaries, digits mark multipliers, and parentheses mark repeated groups — which is exactly why a formula can be parsed algorithmically and always produce one correct, deterministic atom count for every element present.

🎯 When to Use It

  • Finding molar mass for stoichiometry, molarity, or dilution calculations
  • Checking a chemistry homework answer's molecular weight
  • Comparing molar masses across related compounds

📋 Assumptions

  • The formula is entered using standard chemical notation and correct capitalization
  • Atomic weights reflect standard, naturally occurring isotope ratios
  • The formula represents a real, valid chemical compound

⚠️ Limitations

  • Doesn't validate whether a formula represents a chemically real or stable compound
  • Doesn't parse hydrate dot notation (e.g. "·5H2O") automatically — calculate hydration water separately
  • Radioactive elements use a representative isotope mass, not a true natural-abundance average
Walkthrough

Step-by-Step: How to Use the Molecular Weight Calculator

From typing a formula to reading the element breakdown

Enter a chemical formula

Type a formula like H2O, C6H12O6, or Ca(OH)2, using standard capitalization for element symbols.

Click "Calculate"

The calculator parses every element and subscript in the formula, including nested parentheses.

Read the molar mass and breakdown

See the total molar mass in g/mol, plus each element's individual atom count and mass contribution.

Example

Worked Example

A simple formula and a formula with nested parentheses

Scenario 1 — Glucose (C₆H₁₂O₆)

Step 1 — Carbon: 6 × 12.011 = 72.066 g/mol.
Step 2 — Hydrogen: 12 × 1.008 = 12.096 g/mol.
Step 3 — Oxygen: 6 × 15.999 = 95.994 g/mol.
Step 4 — Total: 72.066 + 12.096 + 95.994 = 180.156 g/mol.
Molar Mass
180.156 g/mol

Scenario 2 — Aluminum Sulfate (Al₂(SO₄)₃)

Step 1 — Expand the parentheses: (SO4) × 3 = 3 sulfur atoms, 12 oxygen atoms.
Step 2 — Aluminum: 2 × 26.982 = 53.964 g/mol.
Step 3 — Sulfur: 3 × 32.06 = 96.18 g/mol.
Step 4 — Oxygen: 12 × 15.999 = 191.988 g/mol.
Step 5 — Total: 53.964 + 96.18 + 191.988 = 342.132 g/mol.
Molar Mass
342.132 g/mol
Reference

Common Element Atomic Weights

A selection of frequently used elements from the built-in periodic table (standard atomic weights, g/mol)

ElementSymbolAtomic Weight
HydrogenH1.008
CarbonC12.011
NitrogenN14.007
OxygenO15.999
SodiumNa22.990
MagnesiumMg24.305
AluminumAl26.982
SulfurS32.06
ChlorineCl35.45
PotassiumK39.098
CalciumCa40.078
IronFe55.845
CopperCu63.546
ZincZn65.38
SilverAg107.87
GoldAu196.97

This is a short reference list — the calculator itself includes standard atomic weights for all 118 known elements, so any valid formula can be calculated regardless of which elements it contains.

Use Cases

Practical Use Cases for the Molecular Weight Calculator

Where finding a compound's molar mass comes up

🎓

Chemistry homework

Solve molar mass problems and verify answers for any chemical formula.

🧪

Lab solution preparation

Get the exact molar mass needed for a molarity or dilution calculation.

📊

Stoichiometry problems

Find molar masses to convert between grams and moles in a reaction.

🔬

Comparing related compounds

Quickly compare molar masses across different salts, hydrates, or isomers.

📋

Lab report verification

Double-check a molecular weight calculation before submitting coursework.

Pros & Cons

Advantages and Limitations

What this molecular weight calculator does well, and where it has boundaries

✅ Advantages

  • Free, instant, and requires no signup
  • Runs entirely in your browser — no data is sent to a server
  • Parses nested parentheses correctly, like a chemist would by hand
  • Built-in standard atomic weights for all 118 known elements
  • Shows a full element-by-element mass breakdown, not just the total

⚠️ Limitations

  • Doesn't validate whether a formula represents a chemically real compound
  • Doesn't parse hydrate dot notation automatically — calculate water of hydration separately
  • Radioactive elements use a representative isotope mass, not a natural-abundance average
Reference

Common Mistakes and Expert Tips

Get an accurate molar mass calculation

❌ Common Mistakes

  • Wrong capitalization, like typing "co" instead of "Co" — the parser is case-sensitive on the first letter
  • Forgetting parentheses around a repeated group, entering the atoms individually instead
  • Missing a closing parenthesis, causing a parsing error
  • Typing hydrate notation (like ·5H2O) directly, which this calculator doesn't parse automatically

💡 Expert Tips & Best Practices

  • Use the quick-formula chips above the calculator to see correctly formatted examples
  • For hydrates, calculate the anhydrous compound and water separately, then add the two molar masses
  • Double-check the element breakdown table against your expected atom counts
  • Pair this tool with NeftCal's Molarity Calculator to go straight from formula to solution concentration
📝

Summary: This molecular weight calculator parses any chemical formula, including nested parentheses, and computes its molar mass with a full element-by-element breakdown using a built-in 118-element periodic table — free, instant, and entirely client-side. Pair it with the Molarity Calculator for solution concentration work.

FAQ

Frequently Asked Questions

Common questions about calculating molecular weight

How do I calculate molecular weight from a chemical formula?
Multiply each element's standard atomic weight by how many times it appears in the formula, then add up every element's contribution. For water (H2O): (2 × 1.008) + (1 × 15.999) = 18.015 g/mol.
How does this calculator handle parentheses in a formula, like Ca(OH)2?
The calculator parses parentheses the same way a chemist would by hand: everything inside the parentheses is calculated first, then multiplied by the subscript that follows the closing parenthesis. For Ca(OH)2, the (OH) group is multiplied by 2, giving 1 calcium, 2 oxygen, and 2 hydrogen atoms total.
What is the difference between molecular weight and molar mass?
In practice, the terms are used interchangeably for most purposes. Molecular weight technically refers to the relative mass of a single molecule (a dimensionless ratio), while molar mass is the mass of one mole of that substance, expressed in grams per mole (g/mol). Numerically, they have the same value for molecular compounds.
How accurate are the atomic weights this calculator uses?
This calculator uses standard atomic weights consistent with IUPAC-published values for naturally occurring elements. For radioactive elements without a stable isotope mixture, it uses the mass number of the most stable known isotope, shown conventionally in brackets in most periodic tables.
Can I calculate the molecular weight of a formula with multiple parentheses groups, like Al2(SO4)3?
Yes. The calculator supports any number of parentheses groups, including nested ones, and correctly multiplies each group's contents by its trailing subscript before combining everything into the final total.
Does capitalization matter when entering a chemical formula?
Yes. Element symbols always start with one capital letter, optionally followed by one lowercase letter (like Na for sodium or Co for cobalt) — this distinguishes, for example, Co (cobalt) from CO (carbon monoxide, one carbon and one oxygen atom). Always use standard chemical notation when entering a formula.
Learn More

Authoritative Resources on Atomic Weights

Official chemistry standards references to complement this calculator

⚗️ IUPAC — Periodic Table of the ElementsOfficial international standard atomic weights ↗ 🏛️ NIST — Atomic Weights and Isotopic CompositionsU.S. federal reference atomic weight data ↗

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