Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Computer Science
Lesson Topic: Perform calculations to estimate the file size for a bitmap image
Learning Objective/s:
  • Describe how image resolution and colour depth determine the size of an uncompressed bitmap.
  • Apply the formula S = width × height × bits‑per‑pixel to calculate bitmap size in bits.
  • Convert bits to bytes, kilobytes, megabytes and gigabytes accurately.
  • Analyse the effect of changing resolution or colour depth on file size.
  • Solve practice problems that require estimating bitmap file sizes.
Materials Needed:
  • Projector or interactive whiteboard
  • Printed worksheet with practice questions
  • Calculators (or spreadsheet software on computers)
  • Sample bitmap images (printed or digital)
  • Handout summarising the formula and conversion factors
 Introduction:
Begin with a quick question: “How much storage does a photo on your phone actually use?” Link this to prior knowledge of bits, bytes and digital images. Explain that today students will learn a reliable method for estimating bitmap file sizes and will be able to predict storage needs. Success will be shown by correctly completing the worksheet calculations.
Lesson Structure:
  1. Do‑Now (5’) – Students list the conversion values between bits, bytes, KB, MB, GB.
  2. Mini‑lecture (10’) – Explain resolution, colour depth and introduce the formula S = w × h × b.
  3. Guided example (10’) – Work through the 1280 × 720 × 24‑bit example, showing each conversion step.
  4. Pair activity (15’) – Using the worksheet, students calculate sizes for three given images, then compare results.
  5. Whole‑class discussion (5’) – Groups share findings; discuss how changing colour depth or resolution impacts size.
  6. Check for understanding (5’) – Exit ticket: one new image specification, students write the final size in MB.
Conclusion:
Recap the key steps: identify resolution and colour depth, apply the formula, then convert to appropriate units. Collect exit tickets to gauge individual mastery and assign a homework task to estimate the size of a personal photograph using the learned method. Remind students that understanding these calculations helps in planning storage and choosing appropriate image formats.