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Molar Mass Calculator

Chemistry

Calculate molar mass of any compound from its elements. Select up to 3 elements and enter atom counts to get total molecular weight and percent composition.

Reviewed by the thecalcu.com team · Last updated May 15, 2026

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Molar Mass

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This calculator computes your Molar Mass, Element 1 (%), Element 2 (%), Element 3 (%) from the values you enter.

Inputs
Element 1Atom Count 1Element 2Atom Count 2Element 3 (optional)Atom Count 3
Outputs
Molar MassElement 1 (%)Element 2 (%)Element 3 (%)

What is a Molar Mass?

The Molar Mass Calculator computes the molar mass of a compound from its elemental composition. Select up to three elements and enter the number of atoms of each. The calculator sums nᵢ × Aᵢ for each element and returns the total molar mass in g/mol along with the mass percentage of each element.

Molar mass is the most fundamental conversion factor in chemistry, it is the bridge between the macroscopic (grams, which you weigh on a balance) and the microscopic (moles of molecules, which you count by Avogadro's number). Without molar mass, no stoichiometric calculation is possible. For H₂O: molar mass = 2×1.008 + 15.999 = 18.015 g/mol tells you that 18 g of water contains 6.022 × 10²³ molecules. For glucose C₆H₁₂O₆: molar mass = 180.156 g/mol (the default example showing three elements).

The Percent Composition Calculator focuses on elemental percentages and serves as the complementary tool to this one, together they cover both the total mass and the distribution across elements. The Grams to Moles Calculator uses molar mass to convert measured masses to moles for reaction calculations.

Why Use a Molar Mass Calculator?

Adding atomic masses seems simple, but errors accumulate across multiple elements with multiple atoms each. For H₂SO₄: 2×1.008 + 32.06 + 4×15.999 = 98.072 g/mol, easy to miss a factor of 4 on oxygen or confuse S's atomic mass (32.06) with its mass number (32). This calculator uses IUPAC standard atomic masses (not rounded mass numbers) for accuracy.

For organic compounds (C, H, N, O, S), three elements suffice to cover most molecules. For inorganic salts (NaCl, CaCO₃, MgSO₄), two or three elements cover essentially all common examples in NCERT Class 11 and 12 stoichiometry chapters.

Who Should Use This Calculator?

Class 11 and 12 chemistry students solving stoichiometry problems: molar mass is required for every mole↔gram conversion, concentration calculation, and yield problem in NCERT.

JEE Main and Advanced aspirants where molar mass appears in virtually every chemistry calculation, stoichiometry, solution chemistry, electrochemistry, and organic reactions all require accurate molar masses.

Pharmacy students and technologists preparing solutions and calculating drug doses where molar mass determines the weight to dissolve for a target molar concentration.

Industrial chemists and quality control analysts performing batch calculations for chemical synthesis where yield and purity assessments require precise molar masses.

What Insights Does the Molar Mass Calculator Give You?

Molar Mass (g/mol) is the primary output, the mass of one mole of the compound. Used in n = m/M for mole calculations, C = n/V for molarity, and all stoichiometric ratio calculations.

Element 1 (%), Element 2 (%), Element 3 (%) show the mass fraction of each element, the percent composition. Elements high in the compound (by mass) have large percentages. For water: H = 11.19%, O = 88.81%.

How to use this Molar Mass calculator

  1. Select Element 1 from the dropdown (contains all common elements with atomic masses shown). For H₂O, select H.
  2. Enter Atom Count 1, the subscript number in the formula. For H₂O, count = 2.
  3. Select Element 2 and enter Atom Count 2. For H₂O: O, count = 1.
  4. For three-element compounds (H₂SO₄, C₆H₁₂O₆): select Element 3 and enter count.
  5. Read Molar Mass in g/mol. Cross-check: H₂O ≈ 18, NaCl ≈ 58, H₂SO₄ ≈ 98, CaCO₃ ≈ 100.
Show formula & methodology ↓Show less ↑

Formula & Methodology

Molar mass from elemental composition:

M = n₁×A₁ + n₂×A₂ + n₃×A₃ nᵢ = atom count for element i Aᵢ = standard atomic mass (g/mol) from IUPAC 2021 table

Percent composition:

%element_i = (nᵢ × Aᵢ / M) × 100

Worked example, Aspirin (C₉H₈O₄):

C×9, H×8, O×4, three elements.

C: 9 × 12.011 = 108.099 H: 8 × 1.008  =   8.064 O: 4 × 15.999 =  63.996 M = 108.099 + 8.064 + 63.996 = 180.159 g/mol %C = 108.099/180.159 × 100 = 60.00% %H = 8.064/180.159 × 100   =  4.48% %O = 63.996/180.159 × 100  = 35.52%

Aspirin's molar mass of 180.16 g/mol means a 500 mg tablet contains 500/180.16 = 2.78 millimoles of aspirin. Indian generic manufacturers (including the world's largest aspirin producers in Hyderabad's pharma cluster) use this calculation for batch sheet preparation.

Frequently Asked Questions

What is molar mass?
Molar mass (M) is the mass of one mole (6.022 × 10²³ particles) of a substance, in grams per mole (g/mol). For elements, molar mass equals the standard atomic mass in grams per mole. For compounds, it is the sum of the atomic masses of all constituent atoms. Molar mass is numerically equal to molecular mass in unified atomic mass units (amu), but expressed in g/mol, for example, H₂O has molecular mass 18.015 amu and molar mass 18.015 g/mol.
How is molar mass calculated?
Molar mass = Σ(nᵢ × Aᵢ) where nᵢ is the number of atoms of element i and Aᵢ is the standard atomic mass of element i. For H₂SO₄: M = 2×1.008 + 1×32.06 + 4×15.999 = 2.016 + 32.06 + 63.996 = 98.072 g/mol. For C₆H₁₂O₆ (glucose): M = 6×12.011 + 12×1.008 + 6×15.999 = 72.066 + 12.096 + 95.994 = 180.156 g/mol.
What is the difference between molar mass, molecular mass, and formula mass?
Molecular mass: the mass of one molecule in atomic mass units (amu or Da). Formula mass: the mass of one formula unit (used for ionic compounds like NaCl which don't form discrete molecules) in amu. Molar mass: the mass of one mole (6.022 × 10²³ formula units) in g/mol. Numerically, all three are equal: NaCl has molecular/formula mass 58.44 amu and molar mass 58.44 g/mol. The distinction is units and context, molar mass is used in stoichiometric calculations.
How do I use the Molar Mass Calculator?
Select Element 1 from the dropdown and enter its atom count. Select Element 2 and enter its count (leave as 'none' if the compound has only one element). Optionally add Element 3. The calculator returns the total molar mass and the mass percentage contribution of each element. Default: H₂O (H×2, O×1) = 18.015 g/mol.
What are the molar masses of common chemistry compounds?
H₂O (water): 18.015 g/mol. CO₂: 44.009 g/mol. NaCl: 58.44 g/mol. H₂SO₄: 98.072 g/mol. NaOH: 39.997 g/mol. CaCO₃ (calcium carbonate): 100.087 g/mol. C₆H₁₂O₆ (glucose): 180.156 g/mol. C₁₂H₂₂O₁₁ (sucrose): 342.297 g/mol. NH₃ (ammonia): 17.031 g/mol. HCl: 36.461 g/mol. These are among the most commonly used in NCERT and JEE stoichiometry problems.
How is molar mass used to convert between grams and moles?
n (moles) = m (grams) / M (g/mol). Conversely, m = n × M. For example: 98.07 g of H₂SO₄ = 98.07 / 98.07 = 1 mole. 500 g of NaCl = 500 / 58.44 = 8.56 moles. This conversion is the foundation of stoichiometry. The [Grams to Moles Calculator](/grams-to-moles-calculator/) and [Mole Calculator](/mole-calculator/) perform these conversions directly.
What is the molar mass of air?
Dry air is a mixture of N₂ (78.09%), O₂ (20.95%), Ar (0.93%), and CO₂ (0.04%). The effective molar mass = 0.7809 × 28.014 + 0.2095 × 31.998 + 0.0093 × 39.948 + 0.0004 × 44.009 = 21.874 + 6.704 + 0.372 + 0.018 = 28.97 g/mol. Gases lighter than air (M < 28.97) are less dense than air; gases heavier than air (M > 28.97) are denser and accumulate near the floor. This is relevant to LPG vs CNG safety in Indian homes.
Can molar mass be measured experimentally?
Yes, by several methods: (1) For gases: use M = dRT/P from the ideal gas law, the [Molar Mass of Gas Calculator](/molar-mass-of-gas-calculator/) implements this. (2) Colligative property methods, boiling point elevation or freezing point depression: M_solute = Kb × m_solute × 1000 / (ΔTb × m_solvent). (3) Mass spectrometry, the most precise method, measuring the mass-to-charge ratio of ionised molecules. (4) Osmometry, using the Van't Hoff osmotic pressure equation, especially for large biomolecules.
How is molar mass used in analytical chemistry in India?
Pharmaceutical analysis in India (CDSCO guidelines, IP, Indian Pharmacopoeia) extensively uses molar mass for: preparing standard solutions (dissolving exactly n×M grams per litre to make n mol/L), calculating drug potency (active ingredient % × dose / M = moles per dose), and interpreting HPLC results where peak areas relate to molar concentration. Quality control labs at companies like Sun Pharma, Cipla, and Dr. Reddy's routinely use molar mass in method development and release testing.
What is the formula mass of ionic compounds like CaCO₃?
For ionic compounds, we use formula mass (not molecular mass, since no discrete molecules exist), but the calculation is identical. CaCO₃: M = Ca + C + 3×O = 40.078 + 12.011 + 3×15.999 = 40.078 + 12.011 + 47.997 = 100.086 g/mol. CaCO₃ (limestone, marble) with molar mass 100 g/mol is one of the most abundant minerals in India's Deccan Plateau and is the basis of the cement industry. The [Percent Composition Calculator](/percent-composition-calculator/) shows %Ca = 40.0%, %C = 12.0%, %O = 48.0%.