Which Mac tool should I use?
| Tool | Best for | Resize | Quality control | Shows file size |
|---|---|---|---|---|
| Preview | One image, precise result | Any width or height | JPEG Quality slider | Yes, live |
| Finder: Convert Image | Quick batches | Small, Medium, Large, Actual Size | None | Yes, per option |
| Photos: Export | Photos already in your library | Small to Full Size, or Custom | Low to Maximum | No |
| sips in Terminal | Large batches and scripts | Exact long edge | 0–100 or low to best | No |
| Browser compressor | Exact KB target, smaller PNGs | Limit width | 1–100 or target size | Yes |
How do I reduce image size in Preview?
Preview is the most precise built-in option because it does both jobs: fewer pixels (Adjust Size) and stronger compression (the Quality slider when exporting JPEG). Both dialogs show the resulting file size before you save.
- Open the image in Preview and choose Tools > Adjust Size.
- Set the units to pixels, keep Scale proportionally and Resample image ticked, and type a width such as 1600. The Resulting Size line estimates the new size. Click OK.
- Choose File > Export, set Format to JPEG.
- Drag the Quality slider left until the File Size shown under it is where you want it; just below the middle is usually invisible on screen.
- Pick a new name and click Save. Exporting leaves the original file alone.
Export also converts iPhone HEIC photos to JPEG. If you only use Adjust Size and then close the window, Preview saves over the original, so export a copy when you want to keep it.
How do I resize many images with Finder's Convert Image?
- Select the images in Finder, Control-click (or right-click) and choose Quick Actions > Convert Image.
- Pick a Format: JPEG, PNG or HEIF.
- Pick an Image Size: Small, Medium, Large or Actual Size. Each option shows the resulting file size.
- Untick Preserve Metadata to drop location and camera data, then click Convert. New copies appear next to the originals.
Small, Medium and Large are roughly 320, 640 and 1280 pixels across. Large suits email and most websites; if you need 1600 px or a specific quality, use Preview or sips instead.
How do I export smaller photos from the Photos app?
Dragging a photo out of Photos gives you the full-size file. To export a smaller copy, select the photos and choose File > Export > Export [number] Photos. Set Photo Kind to JPEG, JPEG Quality to High or Medium, and Size to Large, or to Custom with a maximum dimension of 1600. Untick Location Information if the photos will be shared publicly.
How do I compress images with sips in Terminal?
sips (scriptable image processing system) ships with macOS and handles hundreds of files in seconds. Open Terminal, cd into the folder, and use:
sips -Z 1600 *.jpgscales every JPEG so its long edge is at most 1600 px. It overwrites the originals.mkdir smallthensips -Z 1600 *.jpg --out smallwrites resized copies into a folder named small instead.sips -s format jpeg -s formatOptions 70 photo.heic --out photo.jpgconverts to JPEG at quality 70.sips -g pixelWidth -g pixelHeight photo.jpgprints the dimensions without changing anything.
How do I compress to an exact size or keep PNG small on a Mac?
None of the built-in tools can aim for a file size such as 200 KB, and they save PNG losslessly, so a large PNG stays large. Open the compressor in Safari or Chrome: type a Target size and it finds the highest quality that fits, or keep PNG as PNG with a reduced color palette (transparency kept). Safari also reads HEIC directly. Everything runs on your Mac; images are never uploaded.
For PNG specifics, see why your PNG file is so large; for whole folders, see bulk compress images. On a PC, the equivalent tools are covered in reduce image size on Windows.