That Blue Square Thing

AQA Computer Science GCSE

This page is up to date for the AQA 8525 syllabus for exams from 2022.

Data Representation – Hexadecimal Numbers

There's another way of counting you need to know about...

Let's start with the idea of number bases

PDF iconNumber bases – what are they and the ones you need to know

PDF iconWhy use hexadecimal – why we use base 16

Hexadecimal Numbers

Hexadecimal numbers use base 16 - so you can use one digit to county up to 15. The letters A to F are added on after 9, so A = 10, B = 11 and so on until F = 15. That gives you 16 possible values - including the 0.

PDF iconHexadecimal intro – a single slide

Hexadecimal isn't used by computers, but it is an easy thing for humans to use when we're trying to talk in binary. And it converts really easily.

Just remember that A = 10.

PDF iconHexadecimal basics – notes on how it all works

PDF iconThe 16 times table – and how not to panic when doing the maths

One really important thing to remember is that the hexadecimal number FF = 255 - which is the same as the 8 bit binary number 11111111. So, 255 is the largest number which can be represented using 8 bit binary (a byte) and a 2 digit hexadecimal number.

Just remember that A = 10 and F = 15. It's really easy to get into thinking that A is 11 and F is 16. It's not! Get this right and hexadecimal is a piece of cake.

Conversions using Hexadecimal

You need to be able to convert from:

PDF iconConverting Hex to Binary/Binary to Hex – the methods

PDF iconQuestions: Hex to Binary/Binary to Hex (answers)

Converting to and from decimal is harder than to and from binary...

PDF iconConverting Hex to Decimal/Decimal to Hex – the methods

PDF iconQuestions: Hex to Decimal/Decimal to Hex (answers)

Here are some photos taken in class which summarise the methods:

Binary to Hex/Hex to Binary

Decimal to Hex/Hex to Decimal


There's likely to be one or two marks on hexadecimal on the exam.

PDF iconHexadecimal questions – some hex conversion questions

PDF iconAnswers – don't cheat, try and work things out first

The BBC Bitesize website has a section on hexadecimalwiki link that you might want to look at. Well worth a look.

In October 2020 I made this video when the school was closed for a week or so due to some virus or other and we had to teach online. It tries to explain everything about hexadecimal so might be helpful for revision.