Calculate file sizes of image

Image file size is calculated using the formula: colour depth x image height (pixels) x image width (pixels). The result is usually in bits and may need converting to bytes or larger units.

Key points

• Image file size = colour depth × image height × image width (pixels).
• Example: 100×200 pixels, colour depth of 24 bits = 100 × 200 × 24 = 480,000 bits = 60,000 bytes = 60 KB.
• Exam Tip:Always show your working and check which UNITS the answer requires (bits, bytes, KB, MB).
• Common Mistake:Forgetting to convert between bits and bytes. Divide by 8 to go from bits to bytes.
• This formula gives the RAW/uncompressed file size — actual file sizes may be smaller due to compression.