Calculate compression ratio and space saved between an original and compressed file size, in either direction, and sanity-check your result against typical real-world ratios for ZIP, video, images, and audio.
| Type | Typical Ratio | Space Saved |
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Compression ratio is the standard way to express how much a compression algorithm shrank a file, and this calculator computes it directly from an original and a compressed file size — whichever two numbers you have, in either direction. It's useful whether you're comparing archive tools, evaluating a new video codec, checking whether a backup job is actually compressing your data, or just curious how much smaller a ZIP or gzip made a folder of files.
Enter the original (uncompressed) size and the compressed size, each with its own unit (KB, MB, or GB). The calculator converts both to a common unit and computes compression ratio = original size ÷ compressed size, expressed as X:1. It also derives space saved percentage = (1 − compressed/original) × 100, and the absolute amount of space saved (original minus compressed). A doughnut chart visualizes the proportion between the two sizes, and a reference table shows typical ratios for common compression scenarios — general-purpose ZIP, gzip on text, H.265 vs H.264 video, JPEG vs PNG images, and FLAC vs WAV audio — so you can see at a glance whether your result is in a normal range or unusually high or low for the data type.
A compression ratio in isolation doesn't tell you much without context — 2:1 is excellent for already-compressed video but disappointing for plain text, which typically compresses 3:1 or better with gzip. Comparing your actual result against typical real-world ratios helps you judge whether an encoder setting, backup tool, or storage format is performing as expected, or whether something (like re-compressing already-compressed data) is limiting your results.
ZIP and similar archivers achieve roughly 2:1 on typical mixed files by finding and removing repeated byte patterns. Gzip on plain text can do better, often 3:1 or higher, because text has a lot of predictable structure and redundancy.
Video, image, and audio codecs use specialized, lossy techniques tuned to human perception. H.265 roughly halves H.264's bitrate at equal quality (~2:1), JPEG can be 5-10× smaller than PNG for photos, and FLAC is about half the size of uncompressed WAV audio while remaining lossless.
A compression ratio of 4:1 means the original is four times the compressed size — equivalent to 75% space saved. Higher ratios and higher percentages both mean better compression; use whichever framing is clearer for your audience.
Common questions about compression ratio
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