# Hexadecimal

You are probably familiar with the idea that the same number can be written down in different ways - as a tally, as a normal digital, as a roman number, or even as binary (which appears in the KS3 National Curriculum for Computing). *Hexadecimal* is a number system that's based on 16s, and it's useful in ICT and computing for representing large numbers (and also because it's easily converted to binary). Hexadecimal appears in most GCSE Computer Science courses, which also require you to convert between denary and hexadecimal.

In a number system based on **ten**s, each column heading (units, tens, hundreds, etc.) is **ten** times the value of the column heading to its right, and you can use one of **ten** values (1-9 and 0) in each position. In a number system based on **sixteen**s, each column heading is **sixteen** times the one to its right, and you can use one of **sixteen** values in each position.

There aren't sixteen different digits, though, so what comes after 9? Well, hexadecimal uses the digits 0-9, followed by the letters A-F. This means that counting in hexadecimal would give the sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F, 10, 11, 12, etc.

You can click the digits below investigate how to make a hexadecimal number. Clicking each digit with the left mouse button increases it by one, and when it gets to 15, it goes back to 0. Clicking the right mouse button (or a long-tap on a touch-screen) decreases the digit by one.

If you change the hexadecimal number so that it reads 00A4, for example, that means that you want ten 16s and four 1s, so the value of 00A4 is 164. It's as simple as that! If you find the letters confusing, you could try starting with the *Abacus* (in base 16).

Click the digits to investigate. Can you make 100? Is there only one pattern of digits that make each number? As you can see, hexadecimal numbers get big quite quickly. What's the maximum value that you can store in a four-digit number like the one above? Does that number look familiar?

Hexadecimal numbers are most commonly used in ICT and computing to represent colours on web-pages, in drawing applications and in programming.

For a more in-depth discussion of number bases, look at the *Number Bases* page in the *Mathematics* section.
You can also
watch videos on number bases on the* AdvancedICT* YouTube channel.