Ledge

How to resize an image on a Mac before you email or upload it

· 6 min read

Open the image in Preview, choose Tools > Adjust Size, type a new width and click OK. For a smaller copy without opening anything, Control-click the file in Finder and choose Quick Actions > Convert Image. Both are built into macOS. The one thing to know before you start is that Preview saves over the file you opened, so work on a duplicate.

Work out what “too big” means

An image can be too big in two different ways, and forms are not always clear about which one they mean.

  • File size, measured in KB or MB. Email services and upload forms cap this.
  • Pixel dimensions, the width and height. Profile pictures, listings and some forms set a maximum here.

To see both, select the file in Finder and press Command-I. Size is near the top, and Dimensions is under More Info. In Preview, Tools > Show Inspector (Command-I) shows the same details.

Reducing the dimensions also reduces the file size, usually by a lot. If a form only limits file size and you want to keep the dimensions, you can lower the JPEG quality instead, which is covered further down.

Resize one image in Preview

  1. In Finder, select the image and press Command-D to duplicate it. Open the copy in Preview.
  2. Choose Tools > Adjust Size.
  3. Make sure Scale proportionally is ticked, so the picture is not stretched.
  4. Set the pop-up menu beside Width and Height to pixels, then type a new width. The height follows.
  5. Leave Resample image ticked. With it off, only the print resolution changes, and the pixel count and file size stay the same.
  6. Read the Resulting Size line at the bottom, which estimates the new file size, then click OK.
  7. Close the window. Preview saves the change automatically.

The Fit into pop-up at the top of the dialog offers common sizes if you do not have an exact number in mind.

If you resized an original by mistake, press Command-Z while the window is still open. After that, File > Revert To > Browse All Versions can take you back.

Resize several images at once

Preview handles a batch in one pass.

  1. Select the images in Finder, Control-click and choose Open With > Preview. They open in one window with thumbnails in a sidebar.
  2. Click a thumbnail and press Command-A to select all of them.
  3. Choose Tools > Adjust Size.
  4. For images of mixed shapes, choose a size from the Fit into pop-up, so each one is scaled to fit inside that box and keeps its own proportions.
  5. Click OK, then close the window to save.

As before, this changes the files you opened, so run it on copies.

The Finder quick action is the safer choice when you do not need exact numbers, because it always writes new files.

  1. Select the images in Finder.
  2. Control-click one and choose Quick Actions > Convert Image.
  3. Keep the format or change it, then set Image Size to Small, Medium, Large or Actual Size.
  4. Click the Convert button.

The copies appear beside the originals, which stay untouched.

Let Mail shrink photos as it sends them

If the goal is only to get photos through email, Apple’s Mail can do the resizing for you.

  1. Start a new message and attach the images.
  2. Look at the right side of the header area, below the Subject line, for the Image Size pop-up menu.
  3. Choose Small, Medium, Large or Actual Size. The Message Size figure beside it updates as you switch.

Mail scales the images inside that message only. The files on your disk are not changed. The setting applies to every image in the message, and it does nothing for PDFs or other attachments. If you write email in a browser, there is no such menu, so resize the files first.

Make the file smaller without changing its dimensions

Sometimes the pixel size is right and only the file is too heavy.

  1. Open a copy of the image in Preview.
  2. Choose File > Export.
  3. Set Format to JPEG and drag the Quality slider to the left. The File Size estimate updates as you go.
  4. Save under a new name.

Format matters as much as quality. Mac screenshots are saved as PNG, which keeps text crisp but makes large files when the screenshot contains a photo. Exporting that kind of screenshot as JPEG often cuts the size sharply. For a screenshot that is mostly text or interface, stay with PNG and reduce the dimensions instead.

If the image is a HEIC photo from an iPhone and the form will not take it at all, the problem is the format, not the size. How to convert HEIC photos to JPEG on a Mac before uploading covers that case.

A Terminal command for a folder of photos

The sips tool that ships with macOS can resize a whole folder. This writes scaled copies into a new folder and leaves the originals alone:

mkdir smaller
sips -Z 1600 *.jpg --out smaller

The -Z option scales each image so that neither side is longer than the number you give, keeping the proportions. Leave off --out and sips changes the files in place, so include it unless you are working on copies.

Keep the resized copies apart from the originals

Resizing leaves you with pairs of files that look identical in a file picker: the full-size photo and its smaller copy, with nearly the same name. Attaching the wrong one is the most common way this job goes wrong, and you only find out when the upload is rejected a second time.

Simple habits help. Put the copies in their own folder, or add a word such as “web” to their names. Before sending, select a file and press Command-I to confirm its dimensions.

Another way is to stage the right files as you make them. With Ledge, drag each resized copy up to the notch at the top of the screen and let go. It lands on a shelf that drops from the notch and stays there until you take it somewhere. When the set is ready, switch to the message or the upload page, open the shelf with Option-Space or a click on the notch, and drag the images in. Only the files you staged are on the shelf, so the full-size originals are not in the mix.

To be plain about the limits: Ledge does not resize, compress or convert images, and it does not read or index your files. It is a place for them to wait between the folder and the destination. There is no account and no cloud, and it needs macOS 14 Sonoma or later. It is free for 14 days, then $19 once.

For the sending step, see How to attach a file to an email in one drag and Batching files for a single upload on a Mac.

Questions

Does resizing remove location data from a photo?

Not by itself. In Preview, choose Tools > Show Inspector, open the GPS tab and click Remove Location Info. In the Convert Image quick action, untick Preserve Metadata.

Which size should I pick for email?

For photos that will only be viewed on a screen, Mail’s Medium or Large is enough. Send Actual Size when the recipient plans to print or edit the picture.