Molar Mass Calculator (2024)

Created by Joanna Śmietańska, PhD

Reviewed by

Łucja Zaborowska, MD, PhD candidate and Adena Benn

Last updated:

Jan 18, 2024

Table of contents:
  • What is molar mass?
  • Molar mass vs. molecular weight
  • How to find the molar mass formula for any compound?
  • Examples of how to calculate the molar masses of NaCl, NaOH and H₂O
  • How to use this molar mass calculator?
  • FAQ

Our molar mass calculator comes to the rescue if you need to quickly check the weight of 1 mole of any element or chemical compound and you are unable to use the periodic table. Simply select one by one the elements from the list and give the number of atoms in their molecular formula to get the molar mass in a flash.

Many similar tools are case-sensitive, so you must carefully enter the formula of the compound by hand to get the result. In our tool, there is no exception whether you want to count the molar mass of CO2 or maybe the molar mass of NaOH – you will get the correct result the first time!

Here we will tell you more about what the molar mass is and how to find the molar mass of any 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, the symbol mol.

One mole is the amount of a substance containing as many molecules (atoms, molecules, ions) as there are atoms in 12 g of the carbon isotope 12C. This fixed number called the Avogadro's constant or Avogadro number (NA), is equal exactly to 6.02214076×1023 elementary objects, which can be atoms, molecules, ions, or electrons. Here read more about how to calculate moles.

Molar mass μ is a physical quantity that tells us what the mass of one mole of a substance is. We can calculate it in a simple way 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 g/mol unit is more commonly used.

Molar mass vs. molecular weight

It may seem as though the two quantities mean the same thing, but this is not true. Molecular weight and molar mass are different quantities, although numerically equal:

  • Molecular weight (or molecular mass) is the mass of a molecule given in the dalton unit (Da) or the unified atomic mass unit (u). This one 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 will be 44.01 g/mol.

Now we see that the values of molar mass and molecular mass are equal, but they have different units and define the mass of the substance slightly differently. Our molecular weight calculator will help you to find the molecular weight efficiently.

How to find the molar mass formula for any compound?

The general molar mass formula of a compound AxByCz involves multiplying the number of atoms by the molar mass of that element and adding the mass of all the elements in the molecule to get the molar mass:

μ=xμA+yμB+zμC\mu = x \cdot \mu_\mathrm{A} + y \cdot \mu_\mathrm{B} + z \cdot \mu_\mathrm{C}μ=xμA+yμB+zμC

How do we know the molar masses of individual atoms? They are assigned to each element in this molar mass calculator or use the periodic table to read them.

Let's calculate the molar mass of glucose. When we want to calculate the molar mass of a selected substance, four steps are enough:

  1. Write down the chemical formula of the glucose: C6H12O6.

  2. Find the molar masses of carbon (C), hydrogen (H), and oxygen (O).

  3. Count the number of atoms of each element in the compound.

  4. Find the molar mass of glucose by multiplying the atomic masses of the atoms and their number, then find the sum:

    μ = 6 × 12.01 g/mol + 12 × 1.0079 g/mol + 6 × 16 g/mol = 180.1548 g/mol

If you know how to calculate molar mass, learn about other ways to express the amount of substances, especially in solutions by visiting our molality calculator and molarity calculator.

🙋 The molar mass of an ion is the same as the sum of the molar masses of the elements belonging to the ion. For example, the molar mass of Fe³⁺ equals Fe or 55.85 g/mol.

Examples of how to calculate the molar masses of NaCl, NaOH and H₂O

We calculate the molar mass of one molecule of a substance by adding up the molar masses of the individual atoms that form the molecule. Equipped with this knowledge, let us calculate the molar mass of NaCl:

μNaCl=122.99g/mol+135.45g/mol=58.44g/mol\small\begin{split}\mu_{\mathrm{NaCl}} &=\space 1 \cdot 22.99 \space \mathrm{g/mol} \\ &\quad\ + 1 \cdot 35.45 \space \mathrm{g/mol} \\ &= \space 58.44 \space \mathrm{g/mol}\end{split}μNaCl=122.99g/mol+135.45g/mol=58.44g/mol

Similarly, we can calculate the molar mass of compounds containing more atoms. For example, the molar mass of NaOH will be:

μNaOH=122.99g/mol+116g/mol+11.0079g/mol=58.44g/mol\small\begin{split}\mu_{\mathrm{NaOH}} &=\space 1 \cdot 22.99 \space \mathrm{g/mol} \\ &\quad\ + 1 \cdot 16 \space \mathrm{g/mol} \\&\quad\ + 1 \cdot 1.0079 \space \mathrm{g/mol} \\ &= \space 58.44 \space \mathrm{g/mol}\end{split}μNaOH=122.99g/mol+116g/mol+11.0079g/mol=58.44g/mol

If there is more than 1 atom of a given type in a molecule, we need to multiply the molar mass of that element by the number of atoms. For example, we calculate the molar mass of water (H2O) as:

μH2O=21.0079g/mol+116g/mol=18.0158g/mol\small\begin{split}\mu_{\mathrm{H_2O}} &=\space 2 \cdot 1.0079 \space \mathrm{g/mol} \\ &\quad\ +1 \cdot 16 \space \mathrm{g/mol} \\ &= \space 18.0158 \space \mathrm{g/mol}\end{split}μH2O=21.0079g/mol+116g/mol=18.0158g/mol

How to use this molar mass calculator?

Finding the molar mass is fairly quick for simple compounds, but if you are using more complex situations, our calculator will be an invaluable help. Let's see how it works by calculating the molar mass of water:

  1. Write down the chemical formula of water: H2O.

  2. Select "Hydrogen(H)" as the first element from the list, and set the number of atoms as 2.

  3. Repeat this. Select "Oxygen (O)" from the list and set the number of atoms as 1.

  4. An additional field will appear in the molar mass calculator if you want to add more elements to the formula.

  5. You have the result, the molar mass of water is 18.0158 g/mol 👏

  6. In the table below the calculation, you will find information about the molar mass of each element and their percentage in the molecule.

FAQ

What are the units for molar mass?

The units of molar mass are grams per mole or g/mol. Molar mass is defined as the mass of one mole of a substance in grams. Sometimes the unit kg/mol is also used.

How can I find the molar mass of a compound?

To find the molar mass of a chosen compound, e.g., molar mass of HCl:

  1. Find the atomic mass of each element in the periodic table.
  2. Count the number of atoms of each element.
  3. Find the molar masses by multiplying the molar mass of the atoms by their number in the HCI, then add them together.

Therefore, the molar mass of HCl is 1 × 1.0079 g/mol + 1 × 35.45 g/mol = 36.4579 g/mol.

What is the molar mass of CO₂?

The molar mass of CO₂ is 44.01 g/mol. To calculate this:

  1. Find molar masses of carbon (12.01 g/mol) and oxygen (16 g/mol).

  2. Multiply the molar mass of each element by the number of atoms in the compound's formula, then add them together:

    (1 × 12.01 g/mol) + (2 × 16 g/mol) = 44.01 g/mol.

What is the molar mass of H₂O?

The molar mass of H₂O is 18.0158 g/mol. To find this, sum up the molar masses of 2 hydrogen atoms and 1 oxygen atom:

2 × 1.0079 g/mol + 12 × 16 g/mol = 18.0158 g/mol.

What is the molar mass of NaCl?

The molar mass of NaCl is 58.44 g/mol. To get this, sum up the molar masses of 1 sodium atom and 1 chlorine atom:

1 × 22.99 g/mol + 1 × 35.45 g/mol = 58.44 g/mol.

Joanna Śmietańska, PhD

Molar Mass Calculator (2024)
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