Converting a PNG to JPEG on a Mac requires no extra software. macOS ships with three tools that handle the job. Preview gives you a compression slider and shows the output file size before you save. Finder's Convert Image quick action handles batches. Terminal's sips command flies through folders of files. Pick the one that fits the moment.

Convert a Single PNG to JPEG in Preview

Preview, the default image viewer on macOS, exports images and lets you control compression. To convert one PNG file:

  1. Open the PNG in Preview.
  2. Go to the menu bar and choose File > Export.
  3. Set the Format pop-up menu to JPEG.
  4. Use the compression slider. It runs from Least to Best, and Preview shows the resulting file size before you save.
  5. Choose a destination and click Save.

JPEG has no transparency. Any transparent areas in the original PNG get flattened during conversion. Those pixels become white (or whatever background color the image uses) in the resulting JPEG.

Export Multiple PNG Files from Preview

Preview also handles several images at once. Open all the PNGs in a single Preview window. Use the sidebar to select the thumbnails you want to convert. Press Cmd+A to select everything. Then choose File > Export Selected Images. In the export window, pick JPEG under the Options section, set the compression slider, and save the copies to a folder.

This works well for a small batch when you want to check file sizes before exporting. The original PNG files stay untouched.

Use Finder's Convert Image Quick Action

Starting with macOS Monterey 12, Finder includes a built-in quick action called Convert Image. It handles batch conversions without opening another application.

Convert images from Finder

  1. In Finder, select one or more PNG files.
  2. Right-click the selected files.
  3. From the context menu, choose Quick Actions > Convert Image.
  4. A dialog appears. Select JPEG as the output format.
  5. Choose an image size: Small, Medium, Large, or Actual Size. Actual Size keeps the original dimensions.
  6. Decide whether to preserve metadata (camera information, date).
  7. Click Convert.

The Convert Image action writes new JPEG files next to the originals in the same folder. It does not replace the PNG files, so you end up with both versions. To check file type or size later, select a file and press Cmd+I (Get Info).

Convert PNG to JPEG with the Sips Command in Terminal

The sips tool (Scriptable Image Processing System) is built into macOS and converts images fast. Reach for it when you need to script the work or process many files at once.

Convert a single file

Open Terminal and run this command, replacing input.png with your file name and output.jpg with the desired output name:

sips -s format jpeg input.png --out output.jpg

Set JPEG compression

To control compression, add the -s formatOptions flag followed by a number. For example, to set compression to 80:

sips -s format jpeg -s formatOptions 80 input.png --out output.jpg

Convert multiple files at once

Use a wildcard to convert all PNG files in a folder:

for f in *.png; do sips -s format jpeg "$f" --out "${f%.png}.jpg"; done

This loop processes each PNG and creates a JPEG with the same base name. The original PNG files are not deleted. As with the other methods, transparent areas in the PNG get flattened in the JPEG output.

Shortcuts for Finder Dialogs

Two shortcuts help when you are working with export or save dialogs:

  • Press Cmd+Shift+. to toggle hidden files in any Finder dialog.
  • Select a file and press Cmd+I (Get Info) to see its kind (PNG or JPEG) and its size.

When to Use Each Method

Each built-in method has its own strengths:

  • Preview: Best when you want to watch the file size change as you adjust compression, or when you need precise control over a small number of files.
  • Finder Convert Image: Fastest for batch conversions without opening an app. Works well for several files at once, but compression control is limited to the preset sizes (Small, Medium, Large, Actual Size).
  • Terminal sips: Fastest for large batches or when you need to integrate conversion into scripts. Compression control comes through the formatOptions parameter.

All three methods keep your original PNG files intact. For a quick conversion with nothing to install, any of them will work.

Transparency and JPEG

JPEG does not support transparency. If your original PNG contains transparent pixels (a logo on a transparent background, for example), those areas fill with a solid color during conversion. The color depends on how the image is constructed; it is usually white. If you need to preserve transparency, keep the original PNG or use a format that supports it, such as PNG itself or GIF.