Calculate image and sound file sizes
Use the given image or sound settings to calculate raw file sizes and convert to the requested units.
This sequence follows Cambridge IGCSE Computer Science 0478, 2026–2028 syllabus Version 6. It covers subject content sections 1.1–1.3 only. The separately published 2029–2031 syllabus is not mapped here. Practice is original, self-checked and does not award an official Cambridge grade. Full timed papers and human subject-teacher review remain outstanding.
Before you begin
- No programming language is required. Be comfortable with place value and multiplication; each lesson introduces the computer-science notation it uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How many bytes are in 1600 bits?
What you will learn
- Calculate image size from resolution and colour depth
- Calculate sound size from rate, resolution, duration and channels
- Convert bits to bytes and binary units without losing units
Write the formula with units
Uncompressed image size in bits = number of pixels×colour depth. For width×height dimensions, pixels=width×height.
Apply and check the rule
Uncompressed sound size in bits = sample rate×sample resolution×duration×number of channels. Sample rate is samples per second, and duration must be in seconds. Divide bits by eight for bytes, then use 1024 for KiB and larger binary units. Ignore headers only when the question says to do so or provides no header information.
Pause and explain
What extra factor is needed for stereo sound compared with mono?
Worked example
Find the size of 60 seconds of 8 kHz, 16-bit, mono audio in KiB, ignoring headers.
Show the worked solution
- Convert 8 kHz to 8000 samples per second.
- Bits=8000×16×60×1=7,680,000 bits; bytes=960,000.
- KiB=960,000÷1024=937.5 KiB.
Answer 937.5 KiB
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A 100×100 image uses 8 bits per pixel. Find its size in bytes, ignoring headers.
Give me a hint
Calculate pixels×depth, then divide by eight.
Compare my reasoning
- Pixels=100×100=10,000.
- Bits=10,000×8=80,000.
- Bytes=80,000÷8=10,000.
10,000 bytes
Look for these in your work
- Pixel count correct
- Bits correct
- Bytes correct
Find the size in bytes of 10 seconds of 4 kHz, 8-bit stereo sound, ignoring headers.
Give me a hint
Use 4000 samples/s, 8 bits/sample, 10 s and 2 channels.
Compare my reasoning
- Bits=4000×8×10×2=640,000 bits.
- Bytes=640,000÷8.
80,000 bytes
Look for these in your work
- kHz converted to Hz
- Stereo factor 2
- Bytes correct
A 5-second mono clip is recorded at 12 kHz and 16-bit resolution. Find the raw size in KiB, then explain one way to reduce it and the cost.
Give me a hint
Calculate bits first; convert through bytes. Change one setting for the explanation.
Compare my reasoning
- Bits=12,000×16×5=960,000.
- Bytes=120,000; KiB=120,000÷1024≈117.19 KiB.
- Reducing sample rate or resolution lowers size but can reduce recorded accuracy.
About 117.19 KiB. A lower sample rate or resolution saves storage but reduces fidelity.
Look for these in your work
- Raw bit count correct
- Conversion correct to two decimals
- Trade-off explained
Common mistakes
- Using kilohertz as if it were hertz
- Forgetting stereo has two channels
- Dividing by 1024 before converting bits to bytes
What can you explain now?
What is the uncompressed image-size formula in bits?
Compare with the explanation
Pixel count×colour depth
Each pixel is represented by the number of bits specified by its colour depth.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
What unit conversions should you apply, in order, when a file-size answer is requested in KiB?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.