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Grams to Moles Calculator

Created by Wojciech Sas, PhD
Reviewed by Bogna Szyk and Jack Bowater
Last updated: Jan 18, 2024

With this grams to moles calculator, you can swiftly find how to calculate grams to moles for any substance. It can also work the other way around as a moles to grams conversion tool! Read on to learn the grams to moles formula, try solving a problem of how to convert grams to moles yourself, and forget having any issues converting g to mol in the future!

🙋 Do you want to learn more about moles? Omni's mole calculator will help you gain knowledge.

How to calculate moles from grams? - Grams to moles formula

To correctly estimate the number of moles, n, of a substance of a specific mass, m, (in grams), you need to follow the grams to moles formula:

n = m / M,


  • M is the molar mass of this material. The unit is typically g/mol.

But wait, what actually is a mole? The mole is the SI unit of measurement for the amount of a substance. In one mole of matter, there are precisely 6.02214085774 × 10²³ atoms, molecules, or anything else. This tremendous value refers to Avogadro's number (feel free to check our Avogadro's number calculator to find more insights). In other words, it's the unit of quantity, similarly to a dozen or a gross.

Anyway, that's quite a lot, isn't it? This is the reason why it's more convenient to know how to convert grams to moles instead of grams to the number of atoms. This grams to moles calculator helps you evaluate the right result in a fraction of a second.

How to use g to mol calculator?

The tool is really user-friendly and pretty straightforward to use:

  1. Pick one of the possible groups of compounds (you can choose one from Common Gases and Liquids, Salts, Acids, Alkalis, Organic, or Pure Metals).

  2. Find the chemical of your desire from the second list. You can also enter any custom value for molar mass.

  3. Input the mass of your substance.

  4. …And that's all! Our grams to moles calculator knows how to do its stuff!

  5. You can also find the total number of molecules (or atoms) in the Advanced mode.

How to convert grams to moles: an example

Take a look at the example of how to calculate moles from grams. Imagine you have 6 liters of pure water:

  1. Find the molar mass of a water molecule (H₂O). It's ca. 18.015 g/mol.

  2. Convert the volume of the water to its mass, assuming that the density of pure water is 998 kg/m³:

    m = 6 l × 998 kg/m³ = 0.006 m³ × 998 kg/m³= 5.988 kg.

  3. It's easier to work with grams, so convert the mass:

    5.988 kg = 5988 g.

  4. As you already know how the grams to moles conversion work, find the number of moles:

    n = 5988 g / 18.015 g/mol = 332.4 mol.

You can always use our grams to moles calculator to check the result!

Knowing how to convert grams to moles may be helpful in numerous chemical tasks, e.g., finding the mole fraction of a solution. There is also a solution to try the mole fraction calculator instead.


How do I convert from gram to moles?

To convert from grams to moles, follow these few simple steps:

  1. Measure the mass of your sample in grams.
  2. Find the molar mass of the substance you are analyzing.
  3. Divide the mass by the molar mass to find the number of moles in your sample.

What is the molar mass?

The molar mass is the mass of a mole of a substance, which corresponds to the quantity of matter that contains an Avogadro's number of atoms or molecules (depending on the substance). Molar masses change widely in the periodic table: a mole of hydrogen weighs only 1.008 g, while a mole of uranium weighs 238.03 g.

How many moles are 100 grams of water?

In 100 grams of water, there are 5.551 moles. To calculate this result:

  1. Calculate the molar mass of water, which is two hydrogen atoms' and one oxygen atom's molar masses combined:
    (2 × 1.008 g/mol) + 15.999 g/mol = 18.015 g/mol.
  2. Divide the mass of your sample by the molar mass:
    100 g / 18.015 g/mol = 5.551 mol.

This is the number of moles in 100 g of water.

How do I calculate the molar mass?

You can find the molar mass with theoretical knowledge or experimentally.

  • To roughly determine the molar mass of an unknown solid in a lab, you can use the colligative properties of solutions.
  • The molar mass of a gas is straightforward to measure, as equal volumes contain equal number of moles.
  • You can calculate the molar mass of a molecule by summing the molar masses of the composing atoms with the help of the periodic table.
Wojciech Sas, PhD
Choose one of the common chemicals or enter your own molar mass value
Common Gases and Liquids
Water (H₂O)
Molar mass
Grams to moles converter
Number of moles
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