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Mole Calculator

Chemistry

Calculate the number of moles from mass and molar mass, or find the number of molecules using Avogadro's number. Step-by-step results for chemistry students and labs.

18 g
g
18.015 g/mol
g/mol

Moles (mol)

0.999
Molecules (×10²³)
6.017
Molar Mass (g/mol)
18.015

This calculator computes your Moles (mol), Molecules (×10²³), Molar Mass (g/mol) from the values you enter.

Inputs
Mass of SubstanceMolar Mass
Outputs
Moles (mol)Molecules (×10²³)Molar Mass (g/mol)

What is a Moles?

The Mole Calculator converts the mass of any chemical substance into the number of moles, and further into the number of individual molecules, using Avogadro's number. The mole (symbol mol) is the SI unit of amount of substance and is one of the seven base SI units. It provides the essential link between the mass of a material you can weigh on a balance and the number of atoms or molecules actually present — a connection that underpins every quantitative chemistry calculation.

One mole of any substance contains exactly 6.02214076 × 10²³ elementary entities (Avogadro's number). This means 18.015 g of water contains 6.022 × 10²³ water molecules, 58.44 g of NaCl contains 6.022 × 10²³ formula units of NaCl, and 12.011 g of carbon contains 6.022 × 10²³ carbon atoms. The molar mass — measured in g/mol — is the conversion factor that connects grams to moles for each specific substance.

Understanding moles is a prerequisite for virtually every topic in quantitative chemistry: stoichiometry, limiting reagent problems, concentration calculations, gas law problems using the ideal gas equation (PV = nRT), and colligative property calculations. Indian students encounter the mole concept in NCERT Class 9 and Class 11, and it is heavily tested in CBSE board exams, JEE Main, JEE Advanced, and NEET.

This calculator requires just two inputs — the mass of the substance in grams and its molar mass in g/mol — and instantly returns the moles, the number of molecules expressed in units of ×10²³, and the molar mass used. Related tools include the Grams to Moles Calculator for a streamlined mass-to-moles conversion and the Molarity Calculator for concentration calculations.

How to use this Moles calculator

  1. Enter the Mass of Substance — type the mass of your chemical sample in the Mass of Substance field, in grams (g). For example, for 36 g of water, enter 36.
  2. Enter the Molar Mass — type the molar mass of the substance in the Molar Mass field, in g/mol. For water (H₂O), this is 18.015 g/mol. Find molar mass values from the periodic table by summing atomic masses for each element in the formula.
  3. Read Moles (mol) — the highlighted primary result shows the number of moles. This is the value to use in balanced equation ratios, concentration formulas, and gas law problems.
  4. Read Molecules (×10²³) — this output shows how many individual molecules are present. Multiply the displayed value by 10²³ for the actual count (e.g., a result of 2.0000 means 2.0 × 10²³ molecules).
  5. Verify via the steps panel — expand the step-by-step working to see both the moles calculation (m ÷ M_r) and the molecules calculation (n × Nₐ) written out explicitly. This is useful for exam working or lab reports.
  6. Use the moles in your next calculation — apply the moles value to stoichiometric ratios, substitute into PV = nRT, or use it in the Molarity Calculator to find the concentration in a given volume.

Formula & Methodology

Step 1 — Moles from mass:

> n = m ÷ M_r

Where:
- n = moles (mol)
- m = mass of substance (g)
- M_r = molar mass (g/mol)

Step 2 — Molecules from moles:

> N = n × Nₐ

Where:
- N = number of molecules (or atoms)
- Nₐ = Avogadro's number = 6.02214076 × 10²³ mol⁻¹

The calculator expresses N as N ÷ 10²³ (i.e., ×10²³ units) to avoid displaying astronomically large raw numbers.

Worked example:

Find the moles and number of molecules in 54 g of water (H₂O, M_r = 18.015 g/mol).

- n = 54 g ÷ 18.015 g/mol = 2.9975 mol ≈ 3 mol
- N = 3 × 6.022 × 10²³ = 18.066 × 10²³ = 1.8066 × 10²⁴ molecules
- Displayed as: Molecules (×10²³) = 18.0664

This tells you that 54 g of water contains approximately 3 moles and about 1.8 × 10²⁴ individual water molecules. In a stoichiometric context, if this water was produced by the combustion of hydrogen (2H₂ + O₂ → 2H₂O), approximately 3 moles of H₂ and 1.5 moles of O₂ were consumed to produce it.

Frequently Asked Questions

A mole is the SI unit for the amount of substance, defined as exactly 6.02214076 × 10²³ elementary entities (atoms, molecules, ions, or other particles). This number is known as Avogadro's number and provides a bridge between the microscopic world of atoms and the macroscopic quantities we measure in the laboratory. One mole of any substance contains the same number of entities, just as one dozen always means twelve, regardless of what is being counted.
The formula is n = m ÷ M_r, where n is the number of moles, m is the mass of the substance in grams, and M_r is the molar mass in g/mol. For example, to find the moles in 36 g of water (M_r = 18.015 g/mol), you calculate 36 ÷ 18.015 = 1.999 mol, which is approximately 2 moles. This relationship is the foundation of all stoichiometric calculations.
Molar mass is the mass of one mole of a substance, expressed in g/mol. For an element, the molar mass equals the relative atomic mass found on the periodic table (e.g., carbon = 12.011 g/mol). For a compound, add the atomic masses of all atoms in one formula unit (e.g., water H₂O = 2 × 1.008 + 15.999 = 18.015 g/mol). The Molecular Weight Calculator, when available, can calculate this automatically from a chemical formula.
Avogadro's number (Nₐ) is 6.02214076 × 10²³ and represents the number of atoms, molecules, or formula units in exactly one mole of a substance. It was defined precisely in 2019 as part of the SI redefinition of base units. The number is so large because atoms and molecules are incredibly small — one mole of hydrogen atoms, for example, would weigh approximately 1 gram.
Multiply the number of moles by Avogadro's number: N = n × 6.02214076 × 10²³. For example, 0.5 mol of water contains 0.5 × 6.022 × 10²³ = 3.011 × 10²³ molecules. The Mole Calculator displays this as molecules ×10²³, so the result 3.0110 means 3.0110 × 10²³ molecules, making very large numbers readable.
Moles is a unit of amount of substance that counts how many formula units you have in macroscopic terms, while molecules refers to the actual count of individual particles. One mole always contains 6.022 × 10²³ molecules (or atoms, for elements). Chemists use moles in calculations because working with individual molecule counts would require handling numbers like 10²³, which are impractically large for everyday arithmetic.
Grams measure mass — how heavy a sample is — while moles measure the amount of substance — how many particles are present. These two quantities are linked through molar mass: moles = grams ÷ molar mass. The same number of grams of two different substances will contain different numbers of moles because they have different molar masses. Converting between grams and moles is one of the most fundamental skills in chemistry.
First, find the moles of your known reactant or product using this calculator (mass ÷ molar mass). Then use the molar ratios from the balanced equation to find the moles of any other species in the reaction. For example, if 18 g of water is produced in a reaction and you need to find moles of oxygen consumed, calculate moles of water first (1 mol), then apply the 2H₂O:1O₂ ratio to find 0.5 mol of O₂ was consumed.
Yes, the Mole Calculator works for any substance — elements, ionic compounds, covalent compounds, or mixtures (as long as you know the effective molar mass). For a pure element like iron (Fe), the molar mass is simply the atomic mass from the periodic table (55.845 g/mol). For a compound, sum the atomic masses of all atoms in one formula unit.
The mole concept is introduced in Class 9 (NCERT Chapter 3 — Atoms and Molecules) and developed further in Class 11 (NCERT Chapter 1 — Some Basic Concepts of Chemistry). It forms the basis for empirical and molecular formula calculations, stoichiometry, concentration calculations, and gas laws. The mole concept is a high-weightage topic in CBSE board exams and is heavily tested in JEE and NEET, appearing in multiple-step problems.
Hydrogen (H) has a molar mass of approximately 1.008 g/mol. Therefore, 1 gram of hydrogen atoms contains 1 ÷ 1.008 ≈ 0.992 moles. However, molecular hydrogen (H₂) has a molar mass of 2.016 g/mol, so 1 gram of H₂ gas contains 1 ÷ 2.016 ≈ 0.496 moles. Always specify whether you mean atomic or molecular hydrogen when setting up the calculation.
Moles, molarity, and volume are related by the formula: moles = molarity × volume (in litres). If you have a 2 M solution and take 0.5 L, you have 2 × 0.5 = 1 mole of solute in that volume. The Mole Calculator finds moles from mass and molar mass; once you have moles, use the [Molarity Calculator](/molarity-calculator/) to find the concentration in a given volume of solution.
Also known as
moles from massmass to molesmole conversionAvogadro calculatorn = m/M