When writing blog posts, I frequently take screenshots on my Mac and embed them directly into my drafts. However, pasting screenshots straight into a post often creates issues: the sheer file size bloats the page load time, and in some cases, upload limits prevent the image from attaching altogether.

Here is a quick look at why Mac screenshots take up so much storage, and how switching the default format to JPG can dramatically reduce file sizes.

Why Are Mac Screenshots So Large?

By default, macOS saves all screenshots in PNG format.

• PNG (Portable Network Graphics): Uses lossless compression to preserve every pixel perfectly. Because no data is discarded, file sizes are naturally much larger.
• JPG / JPEG: Uses lossy compression, discarding imperceptible color data to drastically reduce the overall file footprint.

How to Reduce Mac Screenshot File Sizes

To cut down on storage and bandwidth, you simply need to change the default screenshot format from PNG to JPG.

As shown in the comparison, the exact same screenshot took up 640 KB in PNG format, but dropped to 152 KB in JPG format—roughly a 4x reduction in file size.

Standard blog images rarely require pixel-perfect color preservation. Unless you specifically need lossless quality or transparency, setting your screenshots—whether saved to the Desktop or copied to the clipboard—to JPG is far more practical and efficient.

Step-by-Step: Changing the Default Format via Terminal

macOS manages screenshot settings through the system defaults system. To change the default image type:

1. Press Command (⌘) + Space to launch Spotlight, type Terminal, and press Enter.
2. Paste the following command into the Terminal window and press Enter:
3. Enter “defaults write com.apple.screencapture type jpg” in the Terminal window

How to Revert Back to PNG

If you ever need to restore the original lossless PNG format, run the same command with png at the end:

1. Press Command (⌘) + Space to launch Spotlight, type Terminal, and press Enter.
2. Paste the following command into the Terminal window and press Enter:
3. Enter “defaults write com.apple.screencapture type png” in the Terminal window

Conclusion

Since making this switch, I save all my Mac screenshots directly as JPGs. I can now drop screenshots straight into my blog editor without having to run them through external compression tools first, speeding up my publishing workflow significantly.

Most everyday screenshots—whether for presentation slides, documentation, or chat apps—do not require original raw pixel data. For standard web use and daily communication, switching to compressed JPGs is by far the more practical and lightweight choice.