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Resizing pictures on a Mac is a straightforward process that helps manage file sizes for easier sharing or storage, especially when dealing with large images from your camera or downloads. The main goal of this guide is to resize pictures on a Mac using built-in tools, ensuring you can adjust dimensions without losing quality.

Before you start:

Ensure you have macOS Ventura or later for the latest Preview app features.
Have the image file ready on your Mac, preferably in formats like JPEG or PNG.
Basic familiarity with Finder and the Preview app is helpful.

Warning: Resizing images can reduce their quality if you over-compress them; always work on a copy of the original file to avoid permanent data loss.

How to resize images using Preview on Mac

Follow these simple steps to resize your pictures efficiently with the built-in Preview application.

Open the image file in Preview by double-clicking it in Finder, or right-click the file and select Open With > Preview.
Click the Markup Toolbar button (it looks like a pencil tip in a circle) if it’s not already visible, or go to the menu bar and select Tools > Adjust Size.
In the Adjust Size dialog box, uncheck the Scale proportionally box only if you want to resize width and height independently; otherwise, leave it checked to maintain aspect ratio.
Enter the desired values in the width or height fields—use pixels, inches, or percentages as needed—and Preview will auto-adjust the other dimension.
Under Resolution, set it to 72 pixels/inch for web use or higher for print, then clickOK.
Save the resized image by going to File > Export, choosing a format and quality level, or overwrite the original with File > Save (but back up first).

Pro tip: For batch resizing multiple images, select them all in Finder, open with Preview, then use the sidebar to select and adjust each one quickly without reopening the app repeatedly.

Resizing pictures on your Mac not only saves storage space but also optimizes images for their intended use, like faster website loading or email attachments under size limits. By reducing file sizes without unnecessary quality loss, you maintain visual appeal while improving efficiency in your workflow.

This process is especially valuable for photographers or content creators who handle high-resolution files daily. It prevents bloated hard drives and ensures smooth sharing across devices, ultimately enhancing productivity and organization on your Mac.