Mole Day: celebrating Avogadro's Constant

Anthony Welsh tells us all about mole day and where it first started.

Anthony Welsh
23rd October 2023
Image Credit: Pixabay @Beeki
Holy Moly, you guys! October 23rd Is Upon Us! Mole Day is marked on this day annually and is celebrated by chemists, students, and chemistry enthusiasts globally.

What is a Mole?

Not to be confused with small furry underground dwelling mammals, you may remember moles from chemistry lessons in school. Put simply, a mole is a fundamental unit devised for measuring out quantities - it's like counting things in a super-special way! It's a quantity of anything (yes, literally anything) that is equivalent to the number of atoms present in 12g of carbon-12. That's a lot of atoms, and we call that number Avogadro's Constant, or NA. It's roughly 6.02 x 10^23. We use the mole to measure just about everything in the known universe, except for energy, forces, fields, and sub-atomic particles.

The History of Mole Day

Mole Day is a celebration with a fascinating backstory. It all began thanks to Maury Oehler, a retired science teacher from Praire du Chien, Wisconsin, who in 1991 created a holiday to celebrate the mole. In an interview with NPR, Maury explained, "In chemistry, the mole is probably the most important concept." Mole Day is celebrated on October 23rd because 10 to the 23rd power is Oct. 23, and it lasts from 6:02 a.m. to 6:02 p.m. It's a day filled with chemistry fun and learning!

The official Mole Day website,, describes it best:

"For a given molecule, one mole is a mass (in grams) whose number is equal to the molar mass of the molecule. For example, the water molecule has a molar mass of 18, therefore one mole of water weighs 18 grams. Similarly, a mole of neon has a molar mass of 20 grams. In general, one mole of any substance contains Avogadro's Number of molecules or atoms of that substance. This relationship was first discovered by Amedeo Avogadro (1776-1858) and he received credit for this after his death."

You could have a mole of anything. You could have a mole of an actual mole (common Eurasian mole Talpa europaea).

For Mole-some vibes, you can join other moleheads over at on October 23rd.

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AUTHOR: Anthony Welsh
Head of Online | Comp Sci. student | Newcastle

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