On the next screen, make sure that the option for Scale proportionally is checked (See image below) Once the Photo opens in the Preview App, click on Tools from the top menu bar of your Mac and then click on Adjust Size… option in the drop-down menu.ģ. Note: If you have chosen a different App as your default Photo viewer, then right click on the photo and select Open with > Preview.Ģ. Double click on the Photo that you want to Resize and allow it to open in the Preview app. Resize Photos on Mac Using Preview Appįollow the steps to Resize Photos on Mac using the Preview App.ġ. In case you want to keep the original photo, make a copy of the original photo and then resize the copied photo. Note: When you resize photos using the Preview App, you will end up losing the original photo as it will be replaced by the resized photo. However, you can easily get around this limitation by simply dragging your Photos from Photo app to your Desktop or any Folder on your Mac. The only place where this method does not work is within the Photos App on your Mac.