Molar Mass Calculator — Find the Molar Mass of Any Chemical Compound

What is Molar Mass?

All substances are made up of atoms or molecules. In chemistry, it is crucial to accurately measure their quantities. To determine the number of reactants and products of chemical reactions, we use the SI base unit of the mole (symbol: mol).

One mole is the amount of a substance containing as many elementary entities (atoms, molecules, ions, or electrons) as there are atoms in 12 g of the carbon isotope ¹²C. This fixed number is called Avogadro's constant (N_A) and equals exactly 6.02214076 × 10²³ elementary objects.

Molar mass (μ) is a physical quantity that tells us what the mass of one mole of a substance is. It can be calculated by dividing the mass of the substance (m) by its amount in moles (n):

μ = m / n

The SI unit of molar mass is kg/mol, but the more commonly used unit is g/mol. In the US customary system, molar mass may also be expressed in oz/mol or lb/mol.

Molar Mass vs. Molecular Weight

It may seem as though the two quantities mean the same thing, but they are not identical:

• Molecular weight (or molecular mass) is the mass of a single molecule, expressed in daltons (Da) or unified atomic mass units (u). One atomic mass unit roughly corresponds to the mass of a single proton or neutron. For example, the molecular weight of CO₂ is 44.01 Da (or 44.01 u).
• Molar mass is the mass of one mole of a substance expressed in g/mol. Thus, the molar mass of CO₂ is 44.01 g/mol.

The numerical values of molar mass and molecular mass are equal, but they have different units and define the mass of the substance slightly differently.

How to Find the Molar Mass Formula for Any Compound

The general molar mass formula of a compound A_xB_yC_z involves multiplying the number of atoms of each element by that element's molar mass, then summing the results:

μ = x · μ_A + y · μ_B + z · μ_C

The molar mass of each individual element can be found in the periodic table or selected directly in our calculator.

Examples of Molar Mass Calculations

NaCl — Sodium Chloride (Table Salt)

• Na (Sodium): 1 atom × 22.990 g/mol = 22.990 g/mol
• Cl (Chlorine): 1 atom × 35.453 g/mol = 35.453 g/mol
• Total: 58.443 g/mol

H₂O — Water

• H (Hydrogen): 2 atoms × 1.008 g/mol = 2.016 g/mol
• O (Oxygen): 1 atom × 15.999 g/mol = 15.999 g/mol
• Total: 18.015 g/mol

NaOH — Sodium Hydroxide

• Na (Sodium): 1 atom × 22.990 g/mol = 22.990 g/mol
• O (Oxygen): 1 atom × 15.999 g/mol = 15.999 g/mol
• H (Hydrogen): 1 atom × 1.008 g/mol = 1.008 g/mol
• Total: 39.997 g/mol

C₆H₁₂O₆ — Glucose

• C (Carbon): 6 atoms × 12.011 g/mol = 72.066 g/mol
• H (Hydrogen): 12 atoms × 1.008 g/mol = 12.096 g/mol
• O (Oxygen): 6 atoms × 15.999 g/mol = 95.994 g/mol
• Total: 180.156 g/mol

Unit Systems Supported

Our molar mass calculator supports both metric and US customary measurement systems:

• Metric: g/mol (grams per mole) — most common in chemistry; kg/mol (kilograms per mole) — SI base unit
• US Customary: oz/mol (ounces per mole); lb/mol (pounds per mole)

Conversion factors used:

• 1 g/mol = 0.001 kg/mol
• 1 g/mol ≈ 0.035274 oz/mol
• 1 g/mol ≈ 0.00220462 lb/mol

How to Use This Molar Mass Calculator

1. Select the first element from the dropdown list (all 118 elements are available).
2. Enter the number of atoms of that element in your compound.
3. Click Add element to add more elements (up to 5).
4. Choose the output unit: g/mol, kg/mol, oz/mol, or lb/mol.
5. Click Calculate to get the molar mass instantly.

You can also use the quick presets (NaCl, H₂O, NaOH, CO₂, Glucose) to fill in the form automatically.

Frequently Asked Questions

What is the molar mass of water?

The molar mass of water (H₂O) is 18.015 g/mol (2 × 1.008 + 1 × 15.999).

What is the molar mass of NaCl?

The molar mass of sodium chloride (NaCl) is 58.443 g/mol (22.990 + 35.453).

How do I find the molar mass of CO₂?

Carbon dioxide (CO₂): 1 × 12.011 + 2 × 15.999 = 44.009 g/mol.

Is molar mass the same as molecular weight?

Numerically they are equal, but molar mass is expressed in g/mol (mass of one mole of substance), while molecular weight is expressed in Da or u (mass of one molecule). They describe the same property but at different scales.