How to reduce the size of a photo

Do you want to reduce the file size or the pixel size?

It cannot be done within Photos. Photos supports the loss less workflow and will always preserve the original image file in the original quality. If you need a smaller image file, you create it by exporting the image from Photos at a smaller pixel size or file size.

• Select the photo in Photos
• The use the command "File > Export > Export 1 photo
• In the export panel click the "v" to the right pf "Photo Hind: JPEG" to reveal the advanced controls and select the image size and quality.
• Save the file to some folder.

If you want this smaller file in Photos import it to Photos.

Hey there, bobinnaples. 

Welcome to the Apple Support Communities. It’s understandable that you’d want to know how to resize your photos, because knowing how to manage your photos is important. 

In the Photos app, you need to export a photo to resize it. File > Export > Export [number] Photos.

You'll find size options of Small, Medium, Large, Full Size, and Custom

Export photos, videos, and slideshows

You can also use the Preview app to resize photos: Resize, rotate, or flip an image in Preview on Mac

If you have questions, or we have an incorrect understanding of the issue, do not hesitate to reach back out. 

Warmly.