10 (ten) is a positive integer following 9 and preceding 11. Since humans have ten fingers, base 10 (the decimal system) is the leading numeral system used by humans worldwide. Its ordinal form is written "10th" or "tenth".

It is one of few non-single-digit numbers that has its own emoji: 🔟‎

## In googology

Due to its ubiquity as a number base, many googologisms are based on the number ten:

• All the -illion numbers and SI prefixes (deca- in particular is exactly 10)
• Googol, googolplex and their variants
• Megiston
• A large portion of Jonathan Bowers' numbers (aside from those based on 3)
• Almost all of Sbiis Saibian's numbers. Menger sponge is a counterexample.
• In Greek-based number naming systems, 10 is associated with prefix deka-, and with prefix deci- in Latin systems.
• Using Sbiis Saibian's naming system, this number is called monologue.
• Aarex Tiaokhiao coined the names uoonol, 1-noogol, uagnol, ueenol, and uignol for this number.
• Username5243 coined the names goonol, doonol, toonol, tetoonol, penoonol, exoonol, eptoonol, ottoonol and ennoonol for this number, and it's equal to 101 = 101 = 101 = etc. in Username5243's Array Notation.
• Nirvana Supermind coined zero-unol for this number, and it's equal to Q<10,1> in quick array notation.
• Binary198 coined the name aballion for this number, and it's equal to f{10}{10} in hyper-Robin notation.

This is also the base of Saibian's Hyper-E notation ,that is Ea = 10^a.

### Googological functions returning 10

• Fusible numbers: \(m_1(2)=10\)
• In duodecimal, the digit eleven is normally represented by an upside-down 3 and is named "el".

In duodecimal, the digit ten is normally represented by an upside-down 2, or an "X" lookalike and is named "dek".

## As a cash denomination

Some currencies, such as the euro and the United States dollar, have banknotes with this number in the denomination.

Some currencies, such as the Czech koruna, the Israeli new shekel (shekel-wise and Agorot-wise) and the Russian ruble, have coins with this number in the denomination.