Mole & Grams-to-Moles Calculator
Molar mass must be greater than 0
Mass cannot be negative
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Moles cannot be negative
Particle count0 particles
Understanding Moles
What a mole is
A mole is 6.022 × 1023 particles of a substance. It is the bridge between a mass you can weigh and the number of molecules that actually react. To find how many moles you have, divide the mass in grams by the molar mass in grams per mole.
n = m / M
The formula as a triangle
Cover the quantity you want and what is left is the formula. Cover n and you get m / M.
6.022 × 1023
particles in one mole. One mole of water is about 18 mL, roughly a tablespoon, and that spoonful holds 6.022 × 1023 molecules.
A worked example, live
This uses the values in the calculator above. Change the mass or the molar mass and it updates.
n = m / M
Enter a mass and a molar mass above to see this worked out.
Common mistakes
The formula n = m / M is simple. Three things still trip people up.
Atomic mass is one atom from the periodic table. Molar mass is the whole formula added up, so for a compound you cannot just read one element’s value.
Subscripts multiply through the whole group: H₂O has 2 hydrogens, so it’s 2×1.008 + 16.00, not 1.008 + 16.00.
Units have to match: type 500 mg into a grams field and the answer is off by 1000× with no error shown.