Skip to main content

Science & lab

Molecular Weight Calculator

This calculator parses chemical formulas (subscripts, parentheses, hydrates) to molecular weight (MW) in g/mol using IUPAC 2021 atomic weights. Type H2O, NaCl, Mg(OH)2, or CuSO4Β·5H2O, or pick from eleven Common Chemicals presets. Live audit lists element counts, unit masses, and mass percentages; Information hub table appends symbols. Decimal places 2–6 (default 4). MW only; not molarity.

By Jeff Beem

Updated

Settings

Chemical Formula

Case-sensitive. Subscripts (H2O), parentheses (Mg(OH)2), hydrates (CuSO4Β·5H2O).

Common Chemicals

Results

Enter a chemical formula or pick a common compound

How to use this calculator

Set Decimal places, then type a Chemical formula or choose a Common Chemicals preset. The dark Results card shows total molecular weight in g/mol; Live audit lists each element’s count, unit mass, and mass percentage. Use the Information hub table to search IUPAC 2021 weights and click symbols to append them to your formula.

Information hub

Abridged standard atomic weights (IUPAC 2021)

Click an element symbol to append it to your formula. Weights in g/mol.

SymbolNameg/mol
Hydrogen1.008
Helium4.002602
Lithium6.94
Beryllium9.0121831
Boron10.81
Carbon12.011
Nitrogen14.007
Oxygen15.999
Fluorine18.998
Neon20.1797
Sodium22.98976928
Magnesium24.305
Aluminium26.9815384
Silicon28.085
Phosphorus30.973762
Sulfur32.06
Chlorine35.45
Argon39.95
Potassium39.0983
Calcium40.078
Scandium44.955907
Titanium47.867
Vanadium50.9415
Chromium51.9961
Manganese54.938043
Iron55.845
Cobalt58.933194
Nickel58.6934
Copper63.546
Zinc65.38
Gallium69.723
Germanium72.63
Arsenic74.921595
Selenium78.971
Bromine79.904
Krypton83.798
Rubidium85.4678
Strontium87.62
Yttrium88.905838
Zirconium91.224
Niobium92.90637
Molybdenum95.95
Technetium97
Ruthenium101.07
Rhodium102.90549
Palladium106.42
Silver107.8682
Cadmium112.414
Indium114.818
Tin118.71
Antimony121.76
Tellurium127.6
Iodine126.90447
Xenon131.293
Caesium132.905452
Barium137.327
Lanthanum138.90547
Cerium140.116
Praseodymium140.90766
Neodymium144.242
Promethium145
Samarium150.36
Europium151.964
Gadolinium157.25
Terbium158.925354
Dysprosium162.5
Holmium164.930329
Erbium167.259
Thulium168.934219
Ytterbium173.045
Lutetium174.9668
Hafnium178.486
Tantalum180.94788
Tungsten183.84
Rhenium186.207
Osmium190.23
Iridium192.217
Platinum195.084
Gold196.96657
Mercury200.592
Thallium204.38
Lead207.2
Bismuth208.9804
Polonium209
Astatine210
Radon222
Francium223
Radium226
Actinium227
Thorium232.0377
Protactinium231.03588
Uranium238.02891
Neptunium237
Plutonium244
Americium243
Curium247
Berkelium247
Californium251
Einsteinium252
Fermium257
Mendelevium258
Nobelium259
Lawrencium262
Rutherfordium267
Dubnium270
Seaborgium269
Bohrium270
Hassium270
Meitnerium278
Darmstadtium281
Roentgenium281
Copernicium285
Nihonium286
Flerovium289
Moscovium289
Livermorium293
Tennessine293
Oganesson294

Formula blueprint

Parentheses: the multiplier applies to the whole group.

Ca(OH)2=Ca + 2Γ—(O + H)

β†’ 1 Ca, 2 O, 2 H

Formula syntax

  • Element symbols: Case-sensitive, Na β‰  na
  • Subscripts: Numbers after symbols (e.g. H2O)
  • Parentheses: Group with multipliers (e.g. Mg(OH)2)

g/mol vs Da

Molecular weight in g/mol equals the mass in daltons (Da). One mole of molecules has a mass in grams equal to the molecular weight. Labs usually report results in g/mol.

When you need MW

Molecular weight is used for molarity (M = m / (MW Γ— V)), mass-to-mole conversions, stoichiometry, and preparing solutions of known concentration.

Unicode subscripts

The parser accepts both C6H12O6 and C₆H₁₂O₆. Unicode subscripts (₀₁₂₃...) are converted automatically.

Reading your molecular weight result

The dark Results card updates as you type a valid formula. Match decimal places in Settings before copying values.

Example: H2O β†’ 18.0150 g/mol

Type H2O. Total molecular weight 18.0150 g/mol at four decimals. Live audit lists H and O counts, each element’s unit mass (g/mol), and Total mass % (about 11.19% H, 88.81% O).

Example: C6H12O6 (glucose) β†’ 180.1560 g/mol

Click Glucose (C6H12O6) or type the formula. Total 180.1560 g/mol. Live audit shows six carbon, twelve hydrogen, and six oxygen atoms with per-element mass shares summing to 100%.

Molecular weight calculator

Parse chemical formulas to molecular weight in g/mol with IUPAC 2021 atomic weights. Input starts empty until you type or pick a preset.

What this calculator does

Parses subscripts, parenthetical groups, and hydrates (Β· or *), sums (atomic weight Γ— atom count) for each element, and reports total molecular weight in g/mol plus a Live audit table. The Information hub lists abridged IUPAC 2021 weights and appends clicked symbols to the formula field.
  • Limits:
    Standard natural-abundance weights only; not mass spectrometry, isotope labeling, or ion charge states. Abridged element set in the hub table.

How the math works

For each element symbol, multiply the IUPAC 2021 atomic weight by the parsed atom count and add all contributions.
MW=βˆ‘i(AiΓ—ni)MW=\sum_i (A_i\times n_i)
Check: NaCl β†’ 22.990+35.45β‰ˆ58.4422.990+35.45\approx 58.44 g/mol (widget shows 58.4398 at four decimals). H2SO4 β†’ 98.0720 g/mol.

Limits

Does not balance equations, name compounds, or compute molarity. Copy MW into the molarity calculator when you need concentration from mass and volume.

Molecular Weight Calculator FAQ

What columns appear in Live audit?

When the formula parses, the table lists Element, Count, Unit mass (g/mol per element), and Total mass %. Rows highlight when you hover the matching symbol in the Information hub table.

How do parentheses and hydrates work?

Mg(OH)2 β†’ about 58.3190 g/mol (1 Mg, 2 O, 2 H). Hydrates use middle dot or asterisk: CuSO4Β·5H2O or CuSO4*5H2O β†’ about 249.6770 g/mol. Unicode subscripts (e.g. Hβ‚‚O) normalize to ASCII before parsing.

What are the Common Chemicals buttons?

Eleven presets fill the formula field: Water, Glucose, Methane, Sodium chloride, Sulfuric acid, Ethanol, Acetic acid, Calcium carbonate, Magnesium hydroxide, Sodium bicarbonate, Copper sulfate pentahydrate. You can still type any supported formula manually.

Why does element capitalization matter?

Symbols are case-sensitive: CO is carbon monoxide; Co is cobalt. First letter uppercase, second lowercase when present. Invalid symbols show a parser error under the input.

Is molecular weight the same as molar mass?

Same numeric value for stoichiometry: molecular weight in daltons (Da) per molecule equals molar mass in grams per mole (g/mol). This page reports g/mol on the Results card.

What does the Information hub periodic table do?

Search or scroll the IUPAC 2021 abridged table and click a symbol to append it to your formula. Hovering a table row highlights that element in the Live audit when it appears in the current formula.

What do decimal places control?

Settings β†’ Decimal places (default 4, options 2–6) rounds total molecular weight and Live audit unit mass and percentage columns. Very large or tiny values may use scientific notation.

How is this different from the molarity calculator?

This page parses a formula to molecular weight (MW) only. The molarity calculator solves M=m/(MWΓ—V)M=m/(MW\times V) for concentration, mass, or volume when MW is known.

Sources & citations

References used for the calculation method and definitions. Links open in a new tab when available.

[1]
IUPAC β€” Atomic Weights of the Elements 2021

Standard atomic weights used in the abridged table and parser.

Science & Lab Reference Note

Educational Use: These tools use standard scientific formulas and accepted constants. Results are intended for learning, homework, and general reference, not for regulated lab work, industrial processes, or clinical applications.

Verification Recommended: Real-world conditions (purity, temperature, pressure, humidity) affect outcomes. For research, manufacturing, or safety-critical work, confirm with a qualified professional or calibrated lab equipment.

Not Professional Advice: This site does not provide chemical, medical, or engineering advice. All calculations run locally in your browser; no data is stored or transmitted.

Β© 2026 CalcRegistry Reference Last Logic Update: July 2026Free Online Utility Tools