Molar Mass Calculator

Chemistry problems always start the same way: you need to convert between grams and moles. And to do that, you need molar mass.

A molar mass calculator makes it instant. Select your elements, set quantities, add as many as your compound needs — and get the complete molecular weight breakdown, formula, and mass percentage for every atom in the compound.

No periodic table required. No addition errors. No wasted time.

What Is Molar Mass?

Molar mass is the total mass in grams of exactly one mole of a substance — whether that substance is made of atoms, molecules, or ions.

Key facts:

• Unit: Grams per mole (g/mol)

• Symbol: M

• 1 mole = 6.02 × 10²³ particles (Avogadro's number)

• Numerically equal to the atomic or molecular weight listed on the periodic table

• Used to convert between the mass of a substance and its number of moles

Think of it this way: if you could count out exactly 6.02 × 10²³ water molecules and weigh them, they'd weigh 18.015 grams. That's the molar mass of water.

How to Calculate Molar Mass — Step by Step

The 3-Step Method

Step 1 — Identify all elements in the compound Read the chemical formula and note each element and how many atoms of it appear.

Step 2 — Find each element's atomic mass Look up the atomic weight of each element on the periodic table (in g/mol).

Step 3 — Multiply and sum Multiply each element's atomic mass by its quantity of atoms, then add all values together.

Formula:M = Σ (Atomic Mass × Number of Atoms)

How the Molar Mass Calculator Works

The calculator lets you build any molecule from scratch:

Inputs

• 1st Element — select atom from dropdown (e.g., Hydrogen H), enter quantity (e.g., 2)

• 2nd Element — select atom (e.g., Oxygen O), enter quantity (e.g., 1)

• + Add Element — keep adding elements for complex compounds (no limit)

Outputs — Your Molecule Results

• Molar mass — total in g/mol (e.g., 1 mol = 18.0150 g/mol)

• Chemical formula — displayed in Hill notation (carbon first when present, then hydrogen, then other elements alphabetically)

• Element breakdown table showing:

  • Element symbol

  • Quantity of atoms

  • Atomic mass M (g/mol)

  • Mass percentage (%) of each element in the compound

Worked Examples — Step by Step

Example 1 — Water (H₂O)

Elements: 2 Hydrogen + 1 Oxygen

Total Molar Mass = 2.016 + 15.999 = 18.015 g/mol

Mass percentages:

• H = 2.016 ÷ 18.015 × 100 = 11.19%

• O = 15.999 ÷ 18.015 × 100 = 88.81%

Example 2 — Sodium Chloride (NaCl)

Elements: 1 Sodium + 1 Chlorine

Total Molar Mass = 22.990 + 35.453 = 58.443 g/mol

Example 3 — Carbon Dioxide (CO₂)

Elements: 1 Carbon + 2 Oxygen

Total Molar Mass = 12.011 + 31.998 = 44.009 g/mol

Common Molar Masses — Quick Reference

What Is Hill Notation?

The calculator displays your compound's chemical formula in Hill notation — the standard system for writing molecular formulas:

• Carbon (C) is listed first when present

• Hydrogen (H) comes second when carbon is present

• All other elements follow in alphabetical order

For compounds without carbon, all elements are listed alphabetically.

Example: Ethanol is written as C₂H₆O in Hill notation — not H₆C₂O or OC₂H₆.

Fun Fact That'll Make You Laugh 😄

One mole of anything is 602,000,000,000,000,000,000,000 particles.

If you had one mole of dollar bills and tried to spend $1 million per second, it would take you longer than the current age of the universe to spend it all.

Chemistry students calculate with this number like it's perfectly normal. It is not normal. Nothing about Avogadro's number is normal. 😂

FAQs

What is molar mass simply explained?

Molar mass is the weight of one mole (6.02 × 10²³ particles) of a substance, measured in grams per mole (g/mol). It equals the sum of atomic masses of all atoms in the compound's formula.

How do I calculate molar mass step by step?

Identify each element in the formula, find its atomic mass from the periodic table, multiply by the number of atoms, then add everything together. Example: H₂O = (2 × 1.008) + (1 × 15.999) = 18.015 g/mol.

What is the molar mass of water?

The molar mass of water (H₂O) is 18.015 g/mol — made up of 2.016 g/mol from hydrogen (11.19%) and 15.999 g/mol from oxygen (88.81%).

What is the difference between molar mass and molecular weight?

They're numerically the same — but the units differ. Molecular weight is technically dimensionless (a ratio). Molar mass has units of g/mol. In practice, chemists use both terms interchangeably in most calculations.

What is Hill notation in chemistry?

Hill notation is the standard system for writing chemical formulas — carbon first, hydrogen second, then all other elements alphabetically. For compounds without carbon, all elements are listed alphabetically. It ensures consistent, universally readable chemical formulas.