Moles Calculator
Convert between mass and moles using the substance's molar mass. Enter a chemical formula to calculate the molar mass automatically.
Amount of substance
1.000mol
H₂O · 18.015 g/mol
moles = mass ÷ molar mass
18.015 g ÷ 18.015 g/mol = 1.000 mol
- Mass
- 18.015 g
- Molar mass
- 18.015 g/mol
- Amount
- 1.000 mol
Molar mass from the formula
| Element | Atoms | Atomic mass | Contribution |
|---|---|---|---|
| H | 2 | 1.008 | 2.016 |
| O | 1 | 15.999 | 15.999 |
Molar mass: 18.015 g/mol
Want to inspect the formula itself?Open the Molar Mass Calculator to see its complete elemental breakdown.
How it works
Two conversions, one constant
From mass to moles
- Find the substance's molar mass.
- Enter the sample mass.
- Divide mass by molar mass.
n = m ÷ M
- n
- = amount in moles
- m
- = mass
- M
- = molar mass
18.015 g ÷ 18.015 g/mol = 1.000 mol
From moles to mass
Multiply the number of moles by the molar mass.
m = n × M
2.000 mol × 18.015 g/mol = 36.03 g
What is a mole?
A mole is a unit for the amount of substance.
One mole contains exactly 6.02214076 × 10²³ specified entities.
The entities can be atoms, molecules, ions, or formula units depending on the substance.
Concepts
Grams, moles, and the link between them
Moles measure amount, not mass
Grams measure mass. Moles measure amount of substance. The molar mass connects the two.
Why do I need molar mass?
Different substances have different masses per mole. The formula determines the molar mass.
- H₂O → 18.015 g/mol
- CO₂ → 44.009 g/mol
- NaCl → 58.440 g/mol
Why can a formula calculate the molar mass?
The formula tells you how many atoms of each element are present.
2 × 1.008 + 1 × 15.999 = 18.015 g/mol
FAQ
Frequently asked questions
What is a mole?
A mole is a unit of amount of substance equal to exactly 6.02214076 × 10²³ specified entities.
How do I calculate moles from grams?
Divide the mass in grams by the molar mass in grams per mole. n = m ÷ M.
How do I convert moles to grams?
Multiply moles by molar mass. m = n × M.
How do I find molar mass?
Add the atomic masses of all atoms represented by the chemical formula.
Can I use a molar mass I already know?
Yes. Turn on Use molar mass manually and enter the value in g/mol. The formula input is then optional.
Why does this calculator say molar mass instead of molecular weight?
Molar mass is the mass of one mole of a substance, expressed in g/mol. Molecular mass refers to the mass of an individual molecule and is expressed in u or Da. Molar mass works for both molecular substances and ionic compounds such as NaCl.
Does this work for ionic compounds?
Yes. For ionic compounds such as NaCl the formula stands for formula units, and one mole contains 6.02214076 × 10²³ of them.
Is the Avogadro constant exact?
Yes. The SI defines the Avogadro constant as exactly 6.02214076 × 10²³ mol⁻¹.
Why can't I convert particles to moles here?
This tool stays focused on mass and moles. Particle counts, gases, and solutions are separate concepts with their own tools.