The File Size Vector
By default, macOS saves every screenshot you capture as a PNG (Portable Network Graphics) file. While PNG offers lossless compression and perfect image quality, the resulting files are massive—often several megabytes for a single full-screen capture. If you frequently take screenshots to embed in emails, upload to web forums, or share via Slack, these massive PNG files will rapidly consume bandwidth and trigger server upload limits. You must force the operating system to utilize a more efficient, compressed format.
How to Change the Screenshot Format to JPG
Because Apple does not provide a simple dropdown menu for this setting, you must use the Terminal to modify the core configuration file for the screenshot utility.
1. Open the Terminal application (found in Applications > Utilities, or via Spotlight).
2. To instruct the operating system to switch the default rendering engine from PNG to JPG, execute the following command exactly as written, and press Enter:
defaults write com.apple.screencapture type jpg3. The Terminal will execute the command silently, returning to a blank prompt. However, the system’s graphical user interface server is still running on the old settings. You must restart the UI server to force it to read the new configuration.
4. Execute the following command and press Enter:
killall SystemUIServerYour screen may flicker for a fraction of a second as the menu bar reloads. From this moment forward, every time you press Command + Shift + 3 or 4, the resulting file on your Desktop will be a highly compressed, web-friendly `.jpg` file.