Resize several images together in Mac Preview

To resize several images together in Mac Preview, select them in the thumbnail sidebar and choose Tools > Adjust Size. Apple documents this batch workflow in its Preview image resizing guide.

1. Open the images in the same Preview window and show the thumbnail sidebar. Select the thumbnails for every image you want to resize. Check the selection before opening Adjust Size so an unrelated image is not included.
2. Choose Tools > Adjust Size. Enter the pixel width or height you want to use across the selected images. Keep Scale proportionally enabled so Preview calculates the other dimension without stretching the image.
3. Keep Resample image enabled when the goal is to change the number of pixels. Apply the change, then save the images.

Decide whether the target is a maximum width or an exact rectangular size before applying one setting to the whole set. For a gallery that accepts images up to a stated width, proportional scaling can make different shapes fit that width. A form that demands the same width and height for every file is a different task: portrait and landscape sources cannot both keep their original proportions and fill the same rectangle through resizing alone. Separate those images for individual crops rather than stretching them.

For a concrete self-check, open one of the saved images and return to Tools > Adjust Size. Compare its dimensions with the setting you chose. If you used Fit into, Apple notes that one dimension can be smaller than the stated box to preserve proportions. Check another image with a different shape as well. Looking at two shapes reveals whether the result fits the intended boundary without assuming every file has identical width and height.

If the receiving site or document requires both an exact width and an exact height, this proportional batch resize may not meet that requirement for images with different aspect ratios. Review the required dimensions before uploading. Apple also documents cropping in Preview, but cropping changes which parts of an image remain, so inspect the result before treating a crop as a substitute for resizing.

If one output has the wrong dimensions, first check whether it was included in the thumbnail selection. Then check whether Scale proportionally or Resample image was changed. Reopen the source or a retained copy for a clean retry; repeatedly adjusting a file that is already smaller gives you less room to preserve detail.