Quick answer
The amount of substance is n = m ÷ M, and the number of particles is N = n × N_A, with N_A = 6.02214076 × 10²³ mol⁻¹. 36 g of water (M = 18.015) is 1.9983 mol, or 1.2034 × 10²⁴ molecules.
Choose the quantity you know (mass or amount) and enter it. The calculator returns moles, particle count and mass.
Related tools: Mole Fraction Calculator: Mole fraction of one component in a mixture. Percent Yield Calculator: Percent yield of a reaction. Electron Configuration Calculator: Ground-state electron configuration of an element or monatomic ion, with noble-gas shorthand and unpaired electrons.
How to use the Mole Calculator
- Choose start from: From mass, From moles and From number of particles.
- Optionally, enter mass (g) (above 0).
- Optionally, enter amount (mol) (above 0).
- Optionally, enter number of particles (above 0).
- Enter molar mass (g/mol) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Start from | Choose one: From mass; From moles; From number of particles | Starts at From mass |
| Mass (optional) | A number, in g | > 0 |
| Amount (optional) | A number, in mol | > 0 |
| Number of particles (optional) | A number | > 0 |
| Molar mass | A number, in g/mol | > 0 |
Formula and method
Formula
n = m ÷ M; N = n × N_A, N_A = 6.02214076×10²³ mol⁻¹
IEEE-754 double precision; shown to the decimals indicated.
N_A is exact in the 2019 SI.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Start from = From mass; Mass = 36; Molar mass = 18.015.
| Result | Value |
|---|---|
| Amount | 1.998335 mol |
| Number of particles | 1.2034e+24 |
| Mass | 36 g |
Example 2
Inputs: Start from = From moles; Amount = 2.5; Molar mass = 58.44.
| Result | Value |
|---|---|
| Mass | 146.1 g |
| Number of particles | 1.5055e+24 |
| Moles | 2.5 mol |
Example 3
Inputs: Start from = From number of particles; Number of particles = 1.2044e+24; Molar mass = 44.01.
| Result | Value |
|---|---|
| Amount | 1.999953 mol |
| Number of particles | 1.2044e+24 |
| Mass | 88.017943 g |
The first line is the headline result (amount). Below it the mole Calculator lists number of particles and mass, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Worked example
36 ÷ 18.015 = 1.998 mol. Multiplying by 6.022 × 10²³ gives 1.2034 × 10²⁴ molecules. One mole of any substance contains the same number of particles.
Avogadro's number
Since 2019, the Avogadro constant is exactly 6.02214076 × 10²³ mol⁻¹ by definition. Only the fields for the chosen mode are used.
How the result changes with mass
Holding every other input at the first worked example, this table changes only mass. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Mass | Amount | Number of particles | Mass |
|---|---|---|---|
| 18 | 0.999167 mol | 6.0171e+23 | 18 g |
| 36 | 1.998335 mol | 1.2034e+24 | 36 g |
| 72 | 3.996669 mol | 2.4069e+24 | 72 g |
| 144 | 7.993339 mol | 4.8137e+24 | 144 g |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Mass: left empty shows "Enter the mass." beside that field and no result.
- Molar mass: entering "0" shows "Molar mass must be greater than 0." beside that field and no result.
Choosing between the Mole Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Mole Fraction Calculator](/science/mole-fraction-calculator/) | moles of the component and moles of everything else | Mole fraction |
| [Percent Yield Calculator](/science/percent-yield/) | actual yield and theoretical yield | Percent yield |
| [Electron Configuration Calculator](/science/electron-configuration/) | element and charge | Electron configuration of H |
| [Dilution Calculator](/science/dilution-ratio/) | solve for | Final volume V₂ |
| [Molarity Calculator](/science/molarity-calculator/) | solute mass, molar mass and solution volume | Molarity |
Background: chemistry calculations
Most basic chemistry calculations chain three relations: moles n = mass ÷ molar mass, molarity M = n ÷ volume in litres, and dilution C₁V₁ = C₂V₂. Keep units consistent: grams with g/mol, litres with mol/L.
Molar masses come from standard atomic weights, which differ slightly between tables and with the isotopic make-up of a real sample.
Assumptions and limitations
- Only the fields for the chosen mode are used
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for mass and molar mass to confirm this.
Frequently asked questions
How many molecules in a mole?
One mole contains 6.02214076 × 10²³ particles, the Avogadro constant.
What is the mass of one mole of carbon-12?
One mole of carbon-12 has a mass of exactly 12 g by the traditional definition.
How many moles in 90 g of water?
90 g ÷ 18.015 g/mol ≈ 5.0 mol of water.
What does the Mole Calculator calculate?
Convert between mass, moles and number of particles. It returns Amount, Number of particles and Mass.
What formula does the Mole Calculator use?
n = m ÷ M; N = n × N_A, N_A = 6.02214076×10²³ mol⁻¹. N_A is exact in the 2019 SI.
What do I need to enter in the mole Calculator?
You enter Start from and Molar mass (g/mol). Optional: Mass (g), Amount (mol) and Number of particles.
What does the “Start from” option change?
It sets how the mole is worked out. The choices are From mass, From moles and From number of particles.
What is an example of a mole result?
With start from From mass, mass 36 and molar mass 18.015, the amount is 1.998335 mol.
Where does the method come from?
The method follows: CODATA 2018 / SI exact constants.
Related calculators
- Mole Fraction Calculator — Mole fraction of one component in a mixture.
- Percent Yield Calculator — Percent yield of a reaction.
- Electron Configuration Calculator — Ground-state electron configuration of an element or monatomic ion, with noble-gas shorthand and unpaired electrons.
- Molarity Calculator — Concentration of a solution from solute mass, molar mass and volume.
- Average Atomic Mass Calculator — Weighted average of isotope masses.
Sources
- CODATA 2018 / SI exact constants
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.