How to Use File Compression and Why Some Files Don't Get Smaller
We've recently added a new feature to our file converter tool: the ability to compress any file into a ZIP archive. This is a great way to package files for easier storage or sending, but the results of compression can sometimes be confusing. This guide will walk you through how to use the feature and explain the technology behind it.
How to Compress a File
Using our new compression service is as simple as any other conversion. Just follow these steps:
- On the homepage, select the format of the file you wish to compress from the "Convert From" dropdown menu (e.g., TXT, PNG, PDF).
- Upload your file as you normally would.
- In the "Convert To" dropdown menu, select the **ZIP** option.
- Click the "Convert" button. Your file will be compressed, and a ZIP archive containing your file will be downloaded to your device.
What is File Compression?
At its core, file compression is the art of reducing the size of a file by finding and eliminating redundancy. Think of a simple text file that contains the sentence "the cat sat on the mat" one hundred times. An uncompressed file would store that full sentence every single time. A compression algorithm, like the one used in ZIP files, is smart enough to store the sentence just once and then leave a tiny instruction that says, "repeat this 99 more times." This results in a much smaller file.
This process works wonderfully for files with a lot of repetitive data, such as text documents, spreadsheets, or uncompressed image formats like BMP.
Why Don't Some Files Get Smaller When Zipped?
This is a very common question. You might try to zip a JPG image or a PDF document and notice that the resulting ZIP file is almost the same size, or in some cases, even slightly larger. This is not an error! It happens because many modern file formats are already compressed internally.
- JPG/PNG Images: These formats use sophisticated, specialized algorithms to compress photographic and graphical data. They have already done the work of finding and reducing redundancy within the image.
- PDF/DOCX/XLSX Documents: Modern document formats from Adobe and Microsoft also use internal compression to keep their file sizes manageable. A DOCX file, for example, is actually a collection of XML files and other assets that have already been zipped together.
When you try to compress a file that is already compressed, the algorithm can't find any more redundancy to eliminate. The small increase in size you might see comes from the overhead of the ZIP container itself—the small amount of data needed to define the archive structure.
The Bottom Line
Our compression tool is working correctly, but its effectiveness depends on your source file. If you need to package multiple files together or want to shrink uncompressed file types, the ZIP feature is perfect. However, for files that are already in a modern, compressed format, zipping them won't provide much additional benefit in terms of size reduction.