Enter a chemical formula

Type any chemical formula into the Chemical Formula field using standard element symbols — for example H2O, NaCl, or C6H12O6. Subscript numbers are plain digits. Parentheses are supported for groups like Ca(OH)2 or Al2(SO4)3. You can also pick a common substance from the dropdown or click one of the quick preset chips.

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Read the molar mass and element breakdown

The result card instantly displays the molar mass in grams per mole (g/mol) along with a table showing every element's atomic mass, atom count, mass contribution, and percent composition. Switch to the Percent Composition tab to see a colour-coded pie chart of the elemental breakdown.

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Convert between mass and moles

Open the Mole Conversions tab and enter the mass of your sample in grams or the number of moles you are working with. The calculator immediately shows how many moles correspond to that mass, the mass that corresponds to that many moles, and the number of molecules using Avogadro's constant.

Molar Mass

M = Σ (Aᵢ × nᵢ)

M is the molar mass in g/mol. For each element i in the formula, Aᵢ is the standard atomic weight (g/mol, from IUPAC 2021) and nᵢ is the number of atoms of that element. The sum runs over all distinct elements.

Mole–Mass Conversion

n = m / M

n is the amount in moles, m is the mass in grams, and M is the molar mass. Rearranging gives m = n × M. This is the core stoichiometry relationship.

Number of Molecules

N = n × Nₐ

N is the number of molecules, n is the amount in moles, and Nₐ is Avogadro's constant (6.02214076 × 10²³ mol⁻¹, exact by SI definition since 2019).

Percent Composition

% element = (Aᵢ × nᵢ / M) × 100

The mass percent of each element equals its mass contribution divided by the total molar mass, multiplied by 100. The percentages across all elements sum to exactly 100%.

Molar mass The mass of one mole of a substance, expressed in grams per mole (g/mol). Numerically equal to the molecular weight in atomic mass units (u or Da).

Mole (mol) The SI base unit for amount of substance. One mole contains exactly 6.02214076 × 10²³ elementary entities (atoms, molecules, ions, etc.). Named after Amedeo Avogadro.

Avogadro's number (Nₐ) 6.02214076 × 10²³ mol⁻¹ — the number of entities per mole. This value is exact and defined by the 2019 SI revision.

Atomic mass (atomic weight) The weighted average mass of an element's naturally occurring isotopes, expressed in atomic mass units (u). Values are set by IUPAC and updated periodically. This calculator uses IUPAC 2021 values.

Percent composition The proportion of each element's mass in a compound, expressed as a percentage. Calculated as (element mass contribution / molar mass) × 100. Used in stoichiometry and empirical formula determination.

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Water (H₂O)

Most common compound

Formula H2O Mass of sample 18 g

Water has a molar mass of 18.015 g/mol — 2 × 1.008 (hydrogen) + 15.999 (oxygen). Oxygen makes up 88.81% of water's mass by weight despite there being only one oxygen atom, because it is so much heavier than hydrogen. A 18-gram sample is almost exactly 1 mole, containing 6.022 × 10²³ molecules.

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Table Salt (NaCl)

Ionic compound

Formula NaCl Mass of sample 58.44 g

Sodium chloride has a molar mass of 58.44 g/mol — 22.990 (Na) + 35.453 (Cl). Chlorine contributes 60.66% of the mass even though the ratio is 1:1, because it is significantly heavier. A 58.44-gram sample is one mole, giving roughly 6.022 × 10²³ NaCl formula units.

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Glucose (C₆H₁₂O₆)

Organic compound with multiple elements

Formula C6H12O6 Number of moles 0.5

Glucose has a molar mass of 180.156 g/mol — carbon contributes 40.00%, hydrogen 6.71%, and oxygen 53.29%. Despite equal numbers of carbons and oxygens (6 each), oxygen dominates by mass. 0.5 moles of glucose has a mass of 90.08 g and contains 3.011 × 10²³ molecules.

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Sulfuric Acid (H₂SO₄)

Polyatomic compound

Formula H2SO4 Mass of sample 49 g

Sulfuric acid has a molar mass of 98.079 g/mol. Oxygen accounts for 65.25% of its mass (4 atoms × 15.999), sulfur 32.69% (1 atom × 32.065), and hydrogen just 2.06% (2 atoms × 1.008). A 49-gram sample is approximately 0.5 moles, containing about 3.011 × 10²³ molecules.

Molar mass is the bridge between the atomic scale and the laboratory scale. It tells you the mass of exactly one mole of any substance — the same quantity that appears in every stoichiometry equation in chemistry. Whether you are titrating an acid, synthesising a drug, or calculating a reaction yield, converting between grams and moles is the first and most critical step.

How to calculate molar mass

To find the molar mass of a compound, sum the atomic masses of every atom in its formula. For water (H₂O): 2 × 1.008 (H) + 1 × 15.999 (O) = 18.015 g/mol. For glucose (C₆H₁₂O₆): 6 × 12.011 + 12 × 1.008 + 6 × 15.999 = 180.156 g/mol. The atomic masses used are the IUPAC 2021 standard atomic weights — weighted averages over the natural isotopic abundances of each element.

This calculator handles parentheses automatically. Al₂(SO₄)₃ expands to Al₂S₃O₁₂: 2 aluminium + 3 sulfur + 12 oxygen atoms, giving a molar mass of 342.154 g/mol. The same method works for any organic or inorganic formula you can write.

Moles, mass, and Avogadro's constant

The mole is the SI unit for amount of substance. One mole of any substance contains exactly 6.02214076 × 10²³ particles — a number called Avogadro's constant. This value has been exact since the 2019 redefinition of the SI base units.

The relationship between mass, moles, and molar mass is simply n = m / M. If you have 36.03 g of water (M = 18.015 g/mol), you have 2.000 moles, which contains 1.204 × 10²⁴ molecules. Rearranging: m = n × M, so 3 moles of NaCl weighs 3 × 58.44 = 175.32 g.

Percent composition and empirical formulas

Percent composition tells you what fraction of a compound's mass comes from each element. For NaCl: sodium contributes 22.990 / 58.44 × 100 = 39.34%, chlorine 60.66%. These percentages always sum to 100% and are independent of the sample size.

Percent composition is how chemists determine empirical formulas from experimental data: burn a compound, measure how much CO₂ and H₂O form, calculate the mass of each element, convert to moles, and find the simplest whole-number ratio. The molar mass of the empirical formula unit is the smallest repeat unit; the molecular formula scales it to match the true molar mass measured by mass spectrometry.

Common uses in chemistry

Molar mass appears in virtually every quantitative chemistry problem. In stoichiometry, balanced equations relate moles of reactants and products — converting measured gram quantities to moles is the first step. In solution chemistry, molarity (mol/L) requires knowing the molar mass to dissolve the right number of grams. In gas law problems, the ideal gas law PV = nRT uses moles. Pharmacology uses molar mass to relate drug concentrations between mass-based (mg/mL) and molar (μM, nM) units. Polymer science uses it to characterise repeat unit size.

What is the difference between molar mass and molecular weight?+

Molar mass (g/mol) and molecular weight (u or Da) are numerically identical but dimensionally different. Molar mass is the mass of one mole of a substance — a macroscopic quantity in grams per mole. Molecular weight (relative molecular mass) is the mass of a single molecule relative to one-twelfth the mass of a carbon-12 atom, expressed in dimensionless atomic mass units. For most practical purposes in chemistry they are used interchangeably.

How do I handle parentheses in a chemical formula?+

Type the formula exactly as it appears in a textbook but using plain ASCII characters — no subscript Unicode. Parentheses work normally: Ca(OH)2 means one calcium, two oxygen, and two hydrogen atoms. Nested parentheses also work: Al2(SO4)3 gives 2 Al, 3 S, and 12 O. The subscript after the closing parenthesis multiplies everything inside. If the calculator shows an error, check that every opening parenthesis has a matching closing one and that all element symbols are correctly capitalised (first letter uppercase, rest lowercase).

What atomic masses does this calculator use?+

This calculator uses IUPAC 2021 standard atomic weights with four decimal places of precision. IUPAC (International Union of Pure and Applied Chemistry) publishes updated values as isotopic abundance measurements improve. For most elements the values change in the fourth decimal place or beyond between revisions, which does not affect typical stoichiometry calculations.

Why does my percent composition not add up to exactly 100%?+

Small rounding differences in the displayed percentages are normal. Internally the calculator works with full floating-point precision, and the displayed values are rounded to two decimal places. If you sum the displayed percentages you may see 99.99% or 100.01% due to rounding. The calculation itself is exact.

Can this calculator handle ionic compounds and polyatomic ions?+

Yes. Ionic compounds like NaCl, MgCl2, and CaCO3 are entered just like covalent compounds — type the formula and the calculator sums the atomic masses of all ions. Polyatomic ions with parentheses are supported: Ca(OH)2 and Al2(SO4)3 both parse correctly. The calculator does not distinguish between ionic and covalent bonding; it simply sums atomic masses, which gives the correct molar mass regardless of bond type. For hydrated compounds like CuSO4·5H2O, enter CuSO4 and H2O separately and add the results: 159.609 + 5 × 18.015 = 249.685 g/mol.

Molar Mass Calculator

How to Use This Calculator

Enter a chemical formula

Read the molar mass and element breakdown

Convert between mass and moles

Formula & Methodology

Key Terms Explained

Real-World Examples

Water (H₂O)

Table Salt (NaCl)

Glucose (C₆H₁₂O₆)

Sulfuric Acid (H₂SO₄)

What Is Molar Mass and Why Does It Matter?

How to calculate molar mass

Moles, mass, and Avogadro's constant

Percent composition and empirical formulas

Common uses in chemistry

Frequently Asked Questions

Molar Mass Calculator

How to Use This Calculator

Enter a chemical formula

Read the molar mass and element breakdown

Convert between mass and moles

Formula & Methodology

Key Terms Explained

Real-World Examples

What Is Molar Mass and Why Does It Matter?

How to calculate molar mass

Moles, mass, and Avogadro's constant

Percent composition and empirical formulas

Common uses in chemistry

Frequently Asked Questions

Keep Exploring

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