Moles Calculator (Mass to Moles)

This calculator converts mass to moles, and moles to mass, using the standard chemistry formula n = m / M, where n is the amount of substance in moles, m is mass in grams, and M is molar mass in grams per mole. Choose one of the preset substances, such as water, sodium chloride, glucose, sulfuric acid or several common metals, and its molar mass fills in automatically, or type in your own molar mass for any element or compound you are working with. Switch between Mass to Moles and Moles to Mass mode depending on which value you already know, then enter your mass in grams or your amount in moles. The calculator instantly returns the moles, the corresponding mass, the number of molecules or atoms in scientific notation using Avogadro's number, and the molar mass used in the calculation, alongside a full breakdown showing the formula applied and the mass per particle. It is built for NCEA Level 2 and 3 Chemistry, university coursework and lab preparation, wherever you need to move quickly between grams and moles without reaching for a periodic table by hand. Because it uses IUPAC standard atomic weights, results are accurate for everyday chemistry problems, though very precise laboratory work should account for the specific isotopic composition of your sample.

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Standard chemistry formula  Molar masses sourced from IUPAC atomic weights (2021 table).
n = m / M   |   m = n x M   |   M = m / n

1. Substance

g/mol

2. Calculate

g

Results

Moles
1.0000
mol
Mass
18.0150
grams
Molecules / Atoms
6.022
x 1023 particles
Molar Mass Used
18.015
g/mol

Calculation Breakdown

ModeMass to Moles
Formulan = m / M
Mass (m)18.0150 g
Molar mass (M)18.015 g/mol
Moles (n)1.0000 mol

Particle Count

Avogadro's number (NA)6.02214 x 1023
Moles calculated1.0000 mol
Particles (n x NA)6.022 x 1023
Mass per particle-
SubstanceWater (H2O)
Result: 18.015 g of water (H2O) contains 1.0000 mol.

How to Calculate Moles from Mass

The mole is the SI unit for amount of substance. The relationship between mass, moles, and molar mass is given by:

n = m / M

Where n is the number of moles (mol), m is the mass in grams (g), and M is the molar mass in grams per mole (g/mol). Rearranging gives you mass (m = n x M) or molar mass (M = m / n).

Worked Example

How many moles are in 18.015 g of water (H2O)?

  1. Find the molar mass of water: H2O = (2 x 1.008) + (1 x 15.999) = 2.016 + 15.999 = 18.015 g/mol
  2. Apply the formula: n = m / M = 18.015 / 18.015 = 1.0000 mol
  3. Number of molecules: 1.0000 x 6.02214 x 1023 = 6.022 x 1023 molecules

This matches the calculator's default output exactly.

Finding Molar Mass from the Periodic Table

The molar mass of an element equals its relative atomic mass in g/mol. For a compound, add the molar masses of all atoms in the formula.

SubstanceFormulaMolar Mass (g/mol)Calculation
WaterH2O18.0152(1.008) + 15.999
Sodium chlorideNaCl58.4422.990 + 35.45
Carbon dioxideCO244.0112.011 + 2(15.999)
GlucoseC6H12O6180.1566(12.011) + 12(1.008) + 6(15.999)
Sulfuric acidH2SO498.0792(1.008) + 32.06 + 4(15.999)
Calcium carbonateCaCO3100.08740.078 + 12.011 + 3(15.999)

Avogadro's Number and Particle Count

One mole of any substance contains exactly 6.02214076 x 1023 particles (atoms, molecules, or formula units). This is Avogadro's number (NA). To find the number of particles, multiply moles by NA: particles = n x 6.02214076 x 1023.

Common Conversions

SubstanceMassMolesMolecules
Water (H2O)18.015 g1.000 mol6.022 x 1023
Water (H2O)9.008 g0.500 mol3.011 x 1023
NaCl58.44 g1.000 mol6.022 x 1023
CO244.01 g1.000 mol6.022 x 1023
Glucose (C6H12O6)180.156 g1.000 mol6.022 x 1023

Related Calculators

Sources and method: International Union of Pure and Applied Chemistry (IUPAC), 2021 atomic weights table (doi.org/10.1515/pac-2019-0603). IUPAC SI unit definitions, 2019 revision (mole defined as exactly 6.02214076 x 1023 elementary entities). Formula n = m / M is standard stoichiometry as taught in NCEA Level 2 and 3 Chemistry.

This calculator is for educational use. Molar masses are rounded to three decimal places for most compounds. For precise laboratory work, use IUPAC standard atomic weights for your specific isotopic composition.

Frequently asked questions

How do you calculate moles from mass?

Use the formula n = m / M, where n is moles, m is mass in grams, and M is molar mass in grams per mole (g/mol). For example, 36.03 g of water (molar mass 18.015 g/mol) gives 36.03 / 18.015 = 2.000 mol. The molar mass of an element or compound is found by summing the atomic masses from the periodic table for each atom in the formula.

How do you find the molar mass of a compound?

Add the atomic masses (from the periodic table) of every atom in the chemical formula. For water (H2O): 2 x 1.008 (hydrogen) + 1 x 15.999 (oxygen) = 18.015 g/mol. For sodium chloride (NaCl): 22.990 (Na) + 35.45 (Cl) = 58.44 g/mol. For glucose (C6H12O6): 6 x 12.011 + 12 x 1.008 + 6 x 15.999 = 180.156 g/mol.

How many molecules are in one mole?

One mole contains exactly 6.02214076 x 10^23 particles (atoms, molecules, or formula units). This is Avogadro's number (N_A). So if you have 2 moles of water, you have 2 x 6.022 x 10^23 = 1.204 x 10^24 water molecules. Multiply moles by Avogadro's number to find the number of particles.

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