Introduction
The Mole Calculator helps you quickly convert between moles, mass, and number of particles. In chemistry, a mole is a unit that measures the amount of a substance. One mole equals 6.022 × 10²³ particles, which is known as Avogadro's number. To convert between moles and grams, you need the molar mass of the substance, which you can find on the periodic table. This tool does the math for you so you can focus on solving chemistry problems. Whether you are working on stoichiometry homework or balancing chemical equations, this calculator makes conversions fast and simple.
How to Use Our Mole Calculator
Enter a chemical formula and a mass to find the number of moles, molar mass, number of particles, and elemental composition of any substance. You can also use Direct Molar Mass Mode to solve for any missing value when you know two out of three: mass, molar mass, or moles.
Chemical Formula Mode
Common Compounds: Pick a substance from the dropdown list of over 120 common compounds like water, table salt, or glucose. The formula will fill in for you right away.
Periodic Table Elements: Choose any of the 118 elements from the dropdown if you are working with a single element instead of a compound.
Chemical Formula: Type any chemical formula directly into the text field. The calculator supports simple formulas like H2O and NaCl, compounds with parentheses like Ca(OH)2 or Al2(SO4)3, and even hydrates like CuSO4·5H2O.
Mass: Enter the mass of your substance and pick the unit you are using from the dropdown. You can choose grams, milligrams, kilograms, micrograms, pounds, or ounces.
Direct Molar Mass Mode
Mass: Enter the mass of your substance and select the unit. Leave this field empty if you want the calculator to solve for it.
Molar Mass (Molecular Weight): Enter the molar mass of your substance in grams per mole (g/mol). You can find this value on the periodic table or from a reference source. If you need help determining the molar mass of a compound, our Molecular Weight Calculator can compute it from any chemical formula. Leave this field empty if you want it calculated.
Moles: Enter the number of moles if you already know it. Leave this field empty if you want the calculator to solve for it. The calculator needs at least two of the three values — mass, molar mass, and moles — to find the missing one.
What Is a Mole in Chemistry?
A mole is a unit of measurement used in chemistry to count very large numbers of tiny things like atoms, molecules, or ions. Just like a "dozen" means 12 of something, a mole means 6.022 × 10²³ of something. This huge number is called Avogadro's number. Scientists use the mole because atoms and molecules are far too small and too many to count one by one.
The Mole Formula
The basic relationship between moles, mass, and molar mass is written as:
n = m / M
- n = number of moles (mol)
- m = mass of the substance (grams)
- M = molar mass (grams per mole, or g/mol)
This means if you know any two of these three values, you can always find the third. For example, if you have 36.03 grams of water (H₂O) and water's molar mass is 18.015 g/mol, you have 36.03 ÷ 18.015 = 2 moles of water.
What Is Molar Mass?
Molar mass is the mass of one mole of a substance. You find it by adding up the atomic masses of every atom in a chemical formula. Atomic masses come from the periodic table. For example, water (H₂O) has two hydrogen atoms (1.008 g/mol each) and one oxygen atom (15.999 g/mol), so its molar mass is (2 × 1.008) + 15.999 = 18.015 g/mol. For a dedicated tool that computes molar mass from any formula, try our Molecular Weight Calculator.
How to Convert Between Moles, Mass, and Particles
Once you know the number of moles, you can find how many particles you have by multiplying moles by Avogadro's number:
Number of particles = n × 6.022 × 10²³
So 1 mole of any substance always contains exactly 6.022 × 10²³ particles. Two moles would contain about 1.204 × 10²⁴ particles, and so on. This works for atoms, molecules, ions, or formula units — whatever makes up the substance. When working with very large or very small numbers like these, our Scientific Notation Calculator can help you express and manipulate them more easily.
Why Moles Matter in Stoichiometry
Stoichiometry is the part of chemistry that deals with the amounts of substances in chemical reactions. Balanced chemical equations tell you the ratio of moles of each reactant and product. For instance, when hydrogen reacts with oxygen to form water:
2H₂ + O₂ → 2H₂O
This equation says that 2 moles of hydrogen gas react with 1 mole of oxygen gas to produce 2 moles of water. Without the mole concept, there would be no practical way to measure out the right amounts of chemicals for a reaction. Our Stoichiometry Calculator can help you work through these mole ratios and determine how much of each substance is needed or produced in a balanced equation.
Common Examples of Molar Mass Values
- NaCl (table salt): 58.44 g/mol
- CO₂ (carbon dioxide): 44.01 g/mol
- C₆H₁₂O₆ (glucose): 180.16 g/mol
- H₂SO₄ (sulfuric acid): 98.08 g/mol
- NaOH (sodium hydroxide): 40.00 g/mol
Tips for Accurate Mole Calculations
Always write the correct chemical formula before doing any math. A wrong formula gives a wrong molar mass, which throws off everything else. When working with compounds that have parentheses, like Ca(OH)₂, remember to multiply every atom inside the parentheses by the subscript outside. In this case, there are 2 oxygen atoms and 2 hydrogen atoms from the (OH)₂ group, plus 1 calcium atom. Also, make sure your mass is in grams before dividing by molar mass, or convert units first if you are working in milligrams, kilograms, or pounds.
If your calculations involve solution concentrations, our Molarity Calculator can help you determine the molarity of a solution once you know the moles of solute and the volume of solution. Similarly, if you need to prepare diluted solutions from a stock, our Dilution Calculator will walk you through the process. For problems involving acids and bases, the pH Calculator is useful for converting between hydrogen ion concentration and pH values. And when working with gases at known temperature and pressure, the Ideal Gas Law Calculator lets you find moles, volume, pressure, or temperature using PV = nRT.
For quick arithmetic checks involving significant figures, percent error, or ratios, these tools can help ensure your final answers are reported correctly and with appropriate precision.