chemistry

Mole Calculator

Calculate moles from mass using molar mass, or convert between moles, mass, and number of particles. Essential for stoichiometry.

Reviewed by Christopher FloiedUpdated April 16, 2026

This free online mole calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.

Mass (g)

Molar Mass (g/mol)

How to Use This Calculator

Enter your input values

Fill in all required input fields for the Mole Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.

Review your inputs

Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

Read the results

The Mole Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

Formula Reference

Mole Calculator Formula

See calculator inputs for the governing equation

Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.

When to Use This Calculator

•Use the Mole Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
•Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
•Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
•Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.

About This Calculator

The Mole Calculator is a free, browser-based calculation tool for engineers, students, and technical professionals. Calculate moles from mass using molar mass, or convert between moles, mass, and number of particles. Essential for stoichiometry. It implements standard formulas and supports both metric (SI) and imperial unit systems with automatic unit conversion. All calculations are performed instantly in your browser with no data sent to a server. Use this calculator as a quick reference and sanity-check tool during design, analysis, and learning. Always verify results against primary engineering references and applicable standards for any safety-critical application.

About Mole Calculator

The Mole Calculator is an essential tool for chemistry students and researchers, converting between mass and moles using a substance's molar mass. The mole is chemistry's fundamental counting unit — like a 'chemist's dozen' but for atoms and molecules. One mole contains Avogadro's number (6.022 × 10²³) of particles, bridging the microscopic world of atoms with macroscopic lab measurements. Understanding moles is central to balancing chemical equations, stoichiometry, calculating yields, and all quantitative chemistry. This calculator handles the most common conversion: given mass and molar mass, find moles. It's one of the first calculations every chemistry student learns and one they use throughout their scientific career.

The Math Behind It

The mole is the chemist's counting unit, allowing us to work with meaningful quantities of atoms and molecules. **The Formula**: n = m / M Where: - n = Number of moles - m = Mass in grams - M = Molar mass in g/mol **What is a Mole?** 1 mole = 6.022 × 10²³ particles (Avogadro's number) This is analogous to 'dozen' (12) or 'score' (20) but for atoms/molecules. The number is specifically chosen so that 1 mole of hydrogen atoms has mass 1 g, 1 mole of carbon-12 has mass 12 g, etc. **Molar Mass**: The mass of 1 mole of a substance: - Numerically equal to atomic/molecular weight - Units: grams per mole (g/mol) Examples: - **H atom**: 1.008 g/mol - **C atom**: 12.01 g/mol - **O atom**: 16.00 g/mol - **H₂O**: 2(1.008) + 16.00 = 18.02 g/mol - **NaCl**: 22.99 + 35.45 = 58.44 g/mol - **CO₂**: 12.01 + 2(16.00) = 44.01 g/mol - **Glucose (C₆H₁₂O₆)**: 180.16 g/mol **Calculating Molar Mass of a Compound**: 1. Find atomic mass of each element (from periodic table) 2. Multiply by number of atoms in formula 3. Add together Example: H₂SO₄ - H: 2 × 1.008 = 2.016 - S: 1 × 32.07 = 32.07 - O: 4 × 16.00 = 64.00 - Total: 98.09 g/mol **Why Use Moles?** **Problem**: Chemical reactions happen between SPECIFIC NUMBERS of atoms, not specific weights. But we can't count individual atoms. **Solution**: Use moles. 1 mole of any substance contains the same number of particles (Avogadro's number), just with different masses. **Example reaction**: 2H₂ + O₂ → 2H₂O - 2 moles H₂ react with 1 mole O₂ - 4 g H₂ + 32 g O₂ → 36 g H₂O The moles ratio (2:1:2) tells us how atoms combine. The gram amounts tell us how much of each to use in the lab. **Avogadro's Number**: 6.022 × 10²³ is so large it's hard to comprehend: - Earth's population: ~8 × 10⁹ - A mole of water molecules weighs only 18 grams - A mole of sand grains would cover Earth's surface to 1 km depth - A mole of pennies distributed equally would give each person on Earth billions of dollars **Moles to Mass Conversion**: If you want to weigh out a certain number of moles: Mass = moles × molar mass Example: 0.5 mol of NaCl Mass = 0.5 × 58.44 = 29.22 g **Mass to Moles**: If you have a mass and want to know the moles: Moles = mass / molar mass Example: 10 g of water Moles = 10 / 18.02 = 0.555 mol **Moles to Particles**: Particles = moles × 6.022 × 10²³ Example: 0.5 mol of H₂O Particles = 0.5 × 6.022 × 10²³ = 3.011 × 10²³ molecules **Complete Conversion Chart**: ``` Mass (g) ←→ Moles (mol) ←→ Particles (atoms/molecules) ÷M ×6.022×10²³ ``` **Stoichiometry Applications**: Using moles in balanced equations: **N₂ + 3H₂ → 2NH₃** (Haber process for ammonia) - 1 mole N₂ reacts with 3 moles H₂ - Produces 2 moles NH₃ - Mass: 28 g N₂ + 6 g H₂ → 34 g NH₃ If you have 56 g N₂ (2 moles), you need 6 moles H₂ (12 g) to fully react, producing 4 moles NH₃ (68 g). **Common Molar Masses to Memorize**: | Substance | Molar Mass | |-----------|-----------| | H | 1.008 | | C | 12.01 | | N | 14.01 | | O | 16.00 | | Na | 22.99 | | Al | 26.98 | | S | 32.07 | | Cl | 35.45 | | Ca | 40.08 | | Fe | 55.85 | | Cu | 63.55 | | Zn | 65.38 | | Ag | 107.87 | | Au | 196.97 | | Pb | 207.2 | | H₂O | 18.02 | | CO₂ | 44.01 | | O₂ | 32.00 | | N₂ | 28.02 | | NaCl | 58.44 | | CaCO₃ | 100.09 | | NaOH | 40.00 | | HCl | 36.46 | | H₂SO₄ | 98.09 | | Glucose (C₆H₁₂O₆) | 180.16 | **Molar Mass from Molecular Formula**: For any compound: 1. Count atoms of each element 2. Multiply by atomic masses 3. Sum all products Example: Aspirin (C₉H₈O₄) - C: 9 × 12.01 = 108.09 - H: 8 × 1.008 = 8.064 - O: 4 × 16.00 = 64.00 - Total: 180.15 g/mol **Empirical vs Molecular Formula**: - **Empirical**: Simplest whole-number ratio (CH₂O for sugar) - **Molecular**: Actual composition (C₆H₁₂O₆ for glucose) Molecular is 6 × empirical for glucose. **Practical Example**: How many moles in 100 g of table salt? NaCl: Na (22.99) + Cl (35.45) = 58.44 g/mol Moles = 100 / 58.44 = 1.71 mol How many molecules? 1.71 × 6.022 × 10²³ = 1.03 × 10²⁴ molecules That's over a trillion trillion molecules in a small handful of salt. **Why the Mole?** Without moles, chemistry calculations would be impossible: - Can't count atoms directly - Can't weigh single molecules - Mass is measurable; particles aren't - Moles bridge these worlds perfectly **National Mole Day**: Chemists celebrate Mole Day on October 23 (10/23) from 6:02 AM to 6:02 PM — referencing 6.02 × 10²³. A tradition among chemistry teachers and students since 1991. **Common Mistakes**: 1. **Molar mass vs. atomic mass**: Subtle distinction — numerically same but different concepts 2. **Forgetting to multiply by subscripts**: H₂O has 2 hydrogens 3. **Mixing units**: Must use grams and g/mol 4. **Confusing mass and moles**: They're related but different 5. **Using atomic number instead of atomic mass**: Different concepts! **Units Practice**: Always carry units through calculations: - g ÷ (g/mol) = mol ✓ - mol × (g/mol) = g ✓ - mol × (molecules/mol) = molecules ✓ If units don't cancel correctly, you've made an error.

Formula Reference

Moles from Mass

n = m / M

Variables: n = moles, m = mass (g), M = molar mass (g/mol)

Avogadro's Number

6.022 × 10²³ particles/mol

Variables: Particles per mole

Worked Examples

Example 1: Water Calculation

How many moles are in 50 grams of water (H₂O)?

Step 1:Molar mass of H₂O:

Step 2: H: 2 × 1.008 = 2.016

Step 3: O: 1 × 16.00 = 16.00

Step 4: Total: 18.02 g/mol

Step 5:Moles = mass / molar mass

Step 6:Moles = 50 / 18.02

Step 7:Moles = 2.77

50 g of water = 2.77 moles = 1.67 × 10²⁴ water molecules.

Example 2: Finding Mass

How many grams are in 0.25 moles of sodium chloride (NaCl)?

Step 1:Molar mass NaCl:

Step 2: Na: 22.99

Step 3: Cl: 35.45

Step 4: Total: 58.44 g/mol

Step 5:Mass = moles × molar mass

Step 6:Mass = 0.25 × 58.44

Step 7:Mass = 14.61 g

0.25 moles of NaCl = 14.61 grams. This is how much table salt you'd measure out.

Common Mistakes & Tips

!Forgetting to multiply by the number of atoms in the formula. H₂O has 2 hydrogens, not 1.
!Using atomic number instead of atomic mass. Different concepts — atomic number is proton count.
!Mixing units. Must be grams and g/mol for the formula to work.
!Confusing moles with molar mass. They're different — moles counts particles, molar mass is g/mol.

Related Concepts

Molarity Calculator

Concentration using moles.

Mass Percent

Composition using mass.

pH Calculator

Uses moles for acid-base calculations.

Frequently Asked Questions

What is Avogadro's number?

Avogadro's number is 6.022 × 10²³, the number of particles (atoms, molecules, ions) in one mole of any substance. It's chosen so that 1 mole of carbon-12 atoms has exactly 12 grams of mass. It's named after Italian scientist Amedeo Avogadro, who first proposed that equal volumes of gases contain equal numbers of molecules. Avogadro's number is now defined exactly (not measured) as part of the SI redefinition.

Why do we use moles in chemistry?

Chemical reactions occur between specific numbers of atoms, not specific masses. But we can't count individual atoms. Moles bridge this gap: 1 mole of any substance contains the same number of particles (Avogadro's number), and molar mass lets us convert between mass (measurable) and moles (what matters for reactions). Moles are the foundation of quantitative chemistry.

How do I find the molar mass of a compound?

Add the atomic masses of all atoms in the molecular formula. For each element, multiply its atomic mass by the number of atoms, then sum. Example for glucose (C₆H₁₂O₆): 6(12.01) + 12(1.008) + 6(16.00) = 72.06 + 12.096 + 96.00 = 180.16 g/mol. Use a periodic table for atomic masses.

How do I convert moles to molecules?

Multiply by Avogadro's number (6.022 × 10²³). Example: 0.5 moles × 6.022 × 10²³ = 3.011 × 10²³ molecules. This is a huge number! Just 1 gram of water contains about 3.3 × 10²² water molecules. Chemists rarely work with individual molecules — they use moles because the numbers are manageable.