File Compression Savings Calculator
Compare an original and compressed file size to get the compression ratio, the percentage of space saved and the bytes reclaimed.
How it works
Compression ratio = original ÷ compressed · Space saved % = (1 − compressed ÷ original) × 100
The compression ratio compares how many original bytes fit into each compressed byte — 2.5 : 1 means the file shrank to 40% of its size. Space saved is the complementary figure, the share of the original that disappeared. A higher ratio means better compression, but lossless formats (ZIP, PNG) hit a limit set by the data’s entropy, while lossy formats (JPEG, MP3) trade quality for far higher ratios.
Worked example
A 100 MB file compressed to 40 MB gives a ratio of 100 ÷ 40 = 2.5 : 1. Space saved is (1 − 40 ÷ 100) × 100 = 60%, reclaiming 60 MB.
Frequently asked questions
What does a 2:1 compression ratio mean?
It means the compressed file is half the size of the original — one compressed byte represents two original bytes. Equivalently, you saved 50% of the space.
Is a higher compression ratio always better?
For storage and bandwidth, yes. But lossy codecs reach high ratios by discarding detail, so beyond a point quality suffers. For lossless data (documents, code, archives) the ratio is capped by how repetitive the data is.
Why did my file barely compress?
Already-compressed data — JPEGs, MP4s, ZIPs — has little redundancy left, so re-compressing it yields a ratio close to 1 : 1. Compression works best on text, logs, uncompressed images and databases.
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This calculator is for educational purposes. Double-check important results before acting on them.