Compression Ratio
How much smaller data becomes after compression.
Formula
Variables
Example
100 MB → 25 MB gives a 4:1 ratio
How it works
Compression ratio compares the original size of a file or dataset with its smaller size after compression. It works by dividing the uncompressed size by the compressed size, so a larger result means the data shrank more. For example, if the original file is 10 times bigger than the compressed file, the compression ratio is 10:1.
When to use it
Use this formula when you want to measure how effective a compression method is for files, images, audio, video, or backups. It is also useful when comparing different compression tools or settings on the same data.
Worked example, step by step
Original video size = 48 MB Compressed video size = 12 MB CR = Uncompressed size / Compressed size CR = 48 / 12 CR = 4 Final answer: the compression ratio is 4:1
Common mistakes to avoid
- Reversing the formula and dividing compressed size by uncompressed size
- Using percentages instead of a ratio when the question asks for compression ratio
- Mixing up file size units, such as MB and KB, before calculating
Did You Know?
Text compresses far better than already-compressed JPEG or MP4 files.
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