Compression Ratio Calculator - Calculate ZIP & Archive Compression

Q: Why do some files not compress at all?

Files that are already compressed (like ZIP archives, MP3s, and MP4 videos) have high entropy (randomness) and cannot be significantly reduced by standard dictionary compression algorithms.

What is the Compression Ratio Calculator?

Used by software engineers, system admins, and archivists to benchmark compression algorithms like Zstandard, Brotli, Gzip, and 7-Zip.

How to Use This Tool

Enter original uncompressed file size and final archive size to see ratio, space saved percentage, and density factors.

Formula & Calculation Logic

The mathematical formula used to calculate this conversion is:

Compression Ratio = Uncompressed Size ÷ Compressed Size Space Saved (%) = [1 - (Compressed Size ÷ Uncompressed Size)] × 100

Step-by-Step Example Calculation

Here is a real-world calculation example demonstrating the mathematics:

Example: Original folder 1,200 MB compressed down to 300 MB ZIP Compression Ratio = 1,200 ÷ 300 = 4.00 : 1 (or 400%) Space Saved = [1 - (300 ÷ 1,200)] × 100 = 75.00% space saved

Frequently Asked Questions

For plain text, log files, and source code, ratios of 4:1 to 10:1 (75-90% savings) are common. Pre-compressed files like JPEGs or MP4s typically yield less than 1.05:1 (<5% savings).

Files that are already compressed (like ZIP archives, MP3s, and MP4 videos) have high entropy (randomness) and cannot be significantly reduced by standard dictionary compression algorithms.