KS3 Binary Lesson — Binary, Hexadecimal, ASCII and Image File Sizes

Two lessons’ worth of KS3 data representation: binary place value both ways, binary addition including one that overflows, hexadecimal and why it exists at all, hex colour codes, ASCII, and how to work out the size of an image file.

Teachable by a non-specialist. The explanation pages can be read aloud or projected as they are, the subject knowledge is in the teacher notes rather than assumed, and every task has a worked answer.

Included (print PDF + fully editable PowerPoint, 12 pages):

• Teacher notes, the three misconceptions, and the kilobyte convention to state out loud before anyone asks
• Binary place value, both directions, with sixteen conversions
• Binary addition — four sums, the last of which overflows a byte, and a question about what a computer does about it
• Hexadecimal — the full 0–F table, why one hex digit is exactly four bits, and conversions both ways
• Hex in the wild — colour codes to decode, and ASCII character codes
• Images — pixels, resolution, colour depth, the file-size formula, and a binary picture to colour in
• Exit-ticket plenary, two pages of worked answers, and a scaffolded support version

Every answer checked by machine. Each conversion, trace and calculation was generated programmatically and then checked back against the printed answer key.

Clear layout, generous spacing and dyslexia-aware design throughout, following British Dyslexia Association style guidance.

Curriculum: KS3 computing — “understand how numbers can be represented in binary, and be able to carry out simple operations on binary numbers”, and “understand how data of various types… can be represented and manipulated digitally”.