Mole Day 2026 is on Friday

About Mole Day

Chemists use the mole to count atoms and molecules in amounts big enough to weigh. One mole holds about 6.02 × 10^23 particles, a figure called Avogadro's number after the Italian scientist Amedeo Avogadro, who proposed in 1811 that equal volumes of gases at the same temperature and pressure contain equal numbers of particles. Mole Day takes its timing from that number: written US-style, October 23 is 10/23, echoing the exponent, and the traditional celebration runs from 6:02 a.m. to 6:02 p.m. Because a mole is also a small burrowing animal, the day comes with plenty of stuffed moles and mole jokes.

The National Mole Day Foundation traces the idea to an article in The Science Teacher in the early 1980s about a high school chemistry teacher who made the case for celebrating the day. Maurice Oehler founded the foundation on May 15, 1991, and it became a nonprofit corporation in Wisconsin in 1992. Each year it chooses a theme with matching artwork, and since 1993 a recorded theme song, and it shares classroom ideas with members, most of whom are high school chemistry teachers. A permanent Mole Day exhibit opened in Prairie du Chien, Wisconsin, in 2018, and Oehler died in January 2020.

The number behind the slogan has become more precise over time. Since the 2019 revision of the International System of Units, the mole has been defined by fixing the Avogadro constant at exactly 6.02214076 × 10^23 per mole, so the 6.02 used on Mole Day is a rounded version. The foundation says the day is celebrated mostly in US schools but also abroad, especially in Canada and Australia.

Sources: National Mole Day Foundation: What Is Mole Day?, National Mole Day Foundation: History of the Foundation, BIPM: SI base unit, the mole, NIST: Redefining the Mole. How we check dates.

How to mark Mole Day

• Work out how many moles of water are in a glass: weigh the glass full and empty, then divide the water's mass in grams by 18, the approximate mass of one mole of water.
• Get a feel for Avogadro's number by calculating how long it would take to count to 6.02 × 10^23 at one number per second (roughly 19 quadrillion years).
• Sew or craft a stuffed mole, or design a mole-themed poster that explains a chemistry idea, a long-running classroom tradition.
• Look up the National Mole Day Foundation's theme for the year and use it for a bulletin board, song or class project.
• Run a simple, supervised reaction such as baking soda and vinegar in a bottle capped with a balloon, and discuss how the amounts relate to moles.

Mole Day dates