Your Mac converts PNG to JPG without any download. The built-in Preview app does it in four clicks, the Photos app handles your library, and a Quick Action turns conversion into a single right-click you can run on a whole folder. For exact file sizes or batch jobs, our browser converter handles up to 50 files at once and hits targets like 100KB automatically, all without uploading anything. This guide covers five methods: Preview, Photos, Quick Actions, the Terminal, and the browser. Pick the one that fits how many files you have and whether a form is demanding a specific size.

Why convert PNG to JPG on a Mac

PNG files look perfect but weigh a lot. A single screenshot can run several megabytes, and a folder of them climbs into the gigabytes fast. JPG compresses that down by 60 to 90 percent, which matters when a website rejects oversized uploads, an email bounces an attachment, or your disk fills with duplicate exports. Macs ship with everything needed to make the switch, so you never need Photoshop or a paid app. The catch is that each built-in tool suits a different job, which is why the methods below run from simplest to most powerful.

There is also a compatibility angle. Some older software and certain web platforms reject PNG outright and accept only JPG. Government upload systems, older content tools, and a few social profiles fall into this group. Converting is not always about size; sometimes the destination simply will not take a PNG.

Method 1: convert with Preview

Preview is the fastest way to convert a single PNG on a Mac. It opens by default when you double-click an image, and its Export command writes JPG with a quality slider you control.

Double-click the PNG to open it in Preview.
Click File in the menu bar and choose Export.
Open the Format dropdown and select JPEG.
Drag the Quality slider to balance size against sharpness, then name the file and pick a destination.
Click Save.

The Quality slider is the part most guides skip. For photographs, the middle of the slider is usually invisible to the eye. For screenshots with small text, keep it high. One quirk: Preview does not show the resulting file size before you save, so hitting a precise target means saving, checking in Finder, and trying again. That trial and error is the gap a browser converter with a size target fills.

Method 2: batch convert in Preview

Preview converts multiple PNG files in one pass. The trick is selecting them all before you open the app.

In Finder, hold Command and click every PNG you want to convert.
Right-click the selection, choose Open With, then Preview.
In Preview's sidebar, press Command-A to select every thumbnail.
Click File, then Export Selected Items.
Choose JPEG, set the quality, pick a folder, and click Choose.

This works well for a dozen or two files. Past that, the sidebar gets unwieldy and a Quick Action or the Terminal scales better. Preview leaves your originals untouched, so you end up with both versions; delete the PNGs afterward if you only want the JPGs.

Method 3: convert with the Photos app

The Photos app converts PNG to JPG by exporting, which suits images already in your library rather than loose files in Finder.

Open Photos and select the image or images to convert.
Click File, then Export, then Export Photo.
Set Photo Kind to JPEG.
Choose a quality level from Low to Maximum.
Click Export, pick a destination, and confirm.

Photos shines when the source is a shot that synced from your iPhone, because the export keeps your edits baked in. For a quick one-off on the desktop, though, Preview is faster since Photos wants the image inside your library first.

Method 4: build a right-click Quick Action

A Quick Action turns conversion into a single right-click in Finder, with no app to open. You build it once in Automator and it lives in your menu permanently.

Open Automator and choose Quick Action as the document type.
Set the workflow to receive image files in Finder.
Search the action library for Change Type of Images and drag it in.
Set the resulting type to JPEG. Accept the Copy Finder Items step if you want to keep originals.
Save it with a clear name like Convert to JPEG.

From then on, right-click any PNG, open Quick Actions, and click your action. Select a whole folder first and it runs across every file. This is the closest a built-in Mac tool comes to one-click batch conversion.

Method 5: convert in the Terminal with ImageMagick

ImageMagick converts PNG to JPG from the Terminal, which suits developers and anyone converting hundreds of files by script. Install Homebrew first, then ImageMagick:

brew install imagemagick

Convert a single file:

magick input.png output.jpg

Convert every PNG in the current folder:

magick mogrify -format jpg *.png

To control quality, add a flag. A value of 90 keeps the image close to the original while still shrinking it:

magick input.png -quality 90 output.jpg

The command line handles volume that would choke a graphical app, at the cost of setup and syntax. For a handful of images it is overkill, and none of these desktop tools target an exact size, which is where the browser wins.

Method 6: convert in your browser

A browser converter handles the one job the Mac's built-in tools cannot: hitting an exact file size. Our converter runs entirely in Safari or Chrome through the HTML5 Canvas API, so your files never upload.

Open the converter in your browser.
Drag your PNGs in, or browse to select them. Up to 50 files, each up to 25MB.
Stay in Quality mode, or switch to Target Size and pick a cap like 100KB.
Convert and download, individually or all at once.

Target Size mode is what sets it apart. A visa portal that caps photos at 100KB rejects a 101KB file, and Preview gives you no way to guarantee you land under. The tool runs a binary search across quality levels to find the sharpest image that fits, demonstrated in our 100KB for online forms guide. Because nothing uploads, it is safe for ID documents and contracts.

What happens to transparent PNGs on Mac

Transparency disappears when any tool converts PNG to JPG, because JPG has no alpha channel. Preview and Photos fill transparent areas with white automatically, with no option to change it. That surprises people converting logos, because a logo meant for a coloured background ends up boxed in white. Our converter gives you the control Preview lacks: choose white, black, or any custom colour, or keep transparency by saving as WebP. The transparent background guide explains how to choose.

Which Mac method should you use

Use Preview for one or two loose files with no size limit.
Use Photos for images already in your library or shot on iPhone.
Use a Quick Action for fast, repeatable right-click batch conversion.
Use the Terminal for hundreds of files or scripted workflows.
Use the browser tool when a form demands an exact size or you want a custom transparency fill.

Most people end up using two: Preview for quick desktop conversions and the browser for anything a form is fussy about.

Frequently asked questions

How do I convert PNG to JPG on Mac for free?

Open the PNG in Preview, click File, then Export, choose JPEG, and click Save. Preview is preinstalled on every Mac, so there is no download. For exact sizes, use our free browser converter.

Can I batch convert PNG to JPG on Mac?

Yes, three ways. Preview's Export Selected Items, a Quick Action, and the Terminal all handle multiple files. For browser batches, our tool takes up to 50 at once.

Does converting on Mac reduce quality?

Slightly, because JPG is lossy. At Preview's higher quality settings the difference is invisible at normal viewing distance. The quality guide covers the right settings.

What happens to transparent backgrounds on Mac?

They turn white in Preview and Photos, which offer no fill choice. To pick a different colour or keep transparency, use our converter's fill options or WebP export.

Why is my JPG still too big for a form?

Because Preview's slider does not target a size. Use Target Size mode in the browser, pick 100KB, and a binary search lands the best image under it.

Is Preview or an online converter better?

Preview wins for speed on a single offline file. An online converter wins for exact sizes, custom transparency fills, or batches larger than a dozen.