Make a photo attachment smaller in Mac Preview

To make a photo attachment smaller in Mac Preview, reduce its pixel dimensions with Tools > Adjust Size, save the result, and check the saved image before attaching it. Apple documents proportional scaling and resampling in Preview’s image resizing guide.

1. Open the photo in Preview. If you need to keep the original at its current size, work from a separate copy.
2. Choose Tools > Adjust Size. Enter a smaller width or height and keep the dimensions proportional so the photo does not appear stretched. Use the resampling option when you intend to reduce the number of pixels, rather than only changing the resolution value.
3. Save the resized photo. Reopen the saved file so you inspect the version you plan to send.
4. Click the Info button in Preview’s toolbar and check the new image’s dimensions in Inspector. Preview’s Inspector guide documents this control. Compare the saved dimensions with the original or with the size you entered in Adjust Size.

For the attachment decision, record two numbers from the saved copy: its pixel dimensions and its file size. The first tells you whether the image was resampled as intended; the second is what you compare with the mail service’s stated attachment limit. Preview’s size dialog may show an estimated new size, but the file you actually attach is the one to check. Open it once at the size the recipient is likely to view it, especially if the photo contains text or another small detail that has to remain readable.

Before sending, check the saved file’s size against your email provider’s attachment limit. Smaller pixel dimensions give you a concrete way to verify that resizing occurred, but they do not establish that the file is small enough for a particular email service. If it still exceeds the limit, resize the saved image to smaller dimensions and check the new result again. Reducing dimensions also leaves fewer pixels in the photo, which may matter if the recipient needs a large image.

If the attachment is still too large, start from the retained original and make another copy at smaller dimensions. Changing only a resolution label while leaving the pixel count intact is a poor substitute when the goal is a smaller image file; Apple’s guide identifies Resample image as the control for changing image data. Check the second saved file again before attaching it.