What Is the Biggest Number? 6 Astronomical Contenders

We're going to need a lot more fingers and toes to count up to the biggest number. Ariel Skelley / Getty Images

As a child, when trying to come up with the biggest number possible, you might have said "infinity plus one." While technically infinity is the largest number because you cannot run out of numbers, the biggest numbers that we know of are still difficult to count but a bit more quantifiable.

So, what is the biggest number? Read on to learn about six large numbers.

1. Avogadro's Number

Named after Italian scientist Amedeo Avogadro, Avogadro's number is a key concept in the field of chemistry. The number represents the number of atoms, ions or molecules in one mole of a substance and is approximately 6.02214076 × 10²³ particles per mole.

2. Eddington Number

One of the largest numbers is the Eddington number, which shares a name with a different concept in cycling. The Eddington number (136 x 2²⁵⁶ or 1.57 x 10⁷⁹) is a hypothesis of the total number of protons in the observable universe.

3. Graham's Number

A mathematical proof by mathematician Ronald Graham, Graham's number is an enormous, unimaginably large number. It is a specific example of a "transfinite number," which goes far beyond the realm of everyday understanding.

The number itself is so large that there is not enough space to accurately represent it using standard mathematical notation.

4. Googol

A googol is a large number equal to 10 to the power of 100 (10¹⁰⁰). Mathematician Edward Kasnery introduced the concept, but it was his 9-year-old nephew who named the incredibly large number.

Fun fact: The search engine Google got its name from the phrase "googol."

5. Googolplex

Even larger than googol, googolplex is 10 to the power of a googol (10^googol). We don't recommend trying to write out all those digits by hand.

6. Rayo's Number

Introduced by mathematician Agustín Rayo, Rayo's number is an extremely large number. The definition of Rayo's number is quite intricate and involves formal systems, but the basic idea is to create a number that is so large that you cannot uniquely describe it within a formal mathematical system.

This article was created in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.