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How to reduce a photo's file size before you upload it

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You reduce a photo's file size by lowering its pixel dimensions and saving it in a compressed format such as JPEG or WebP at a sensible quality. For most forms and email attachments, those two steps are enough.

In short

  • A photo's file size depends mostly on its pixel count, its format and its compression quality.
  • Halving the width and height leaves about a quarter of the pixels.
  • Photos are usually far lighter as JPEG or WebP than as PNG.
  • CatTower's image resizer takes one PNG, JPEG or WebP of up to 20 MB and lets you set JPEG and WebP quality from 1 to 100 (85 by default).
  • Images are resized on our server and not stored. Free, with no sign-up.

Shrink it with the image resizer

Why photos are so large

A photo from a recent phone is often around 4,000 px wide and well over 12 megapixels. That is far more than a screen needs, so the file is much heavier than a form or an email attachment calls for.

Three things set the file size: the number of pixels, the format, and, for JPEG and WebP, the compression quality. Changing any one of them helps, but adjusting the pixel size and the format together makes the biggest difference.

Check the requirement first

Find out whether the site limits the file size or the pixel size. "Under 1 MB" is a file size limit; "600 px wide" is a pixel limit. If both are given, match the pixel size first, then lower the quality if the file is still too big.

Check the accepted formats too. A site that only takes JPG may reject a PNG or WebP file whatever its size.

Three ways to make it smaller

  • Lower the pixel size: the biggest win. Halving the width and height leaves about a quarter of the pixels, and the file usually shrinks by about as much. For photos seen on a screen, 1,600–2,000 px on the long edge is often plenty.
  • Change the format: photos saved as PNG are often heavy. JPEG or WebP suit photos, while screenshots full of text and lines can stay sharper as PNG. Transparent areas turn white in JPEG.
  • Lower the quality: bringing JPEG or WebP quality down a little often shrinks the file with no visible change. Go too low and edges turn muddy, so step down gradually and check the result.

Things to watch

A photo you shrink and then enlarge again turns blurry. Keep the original and work on a copy.

If you unlock the aspect ratio and type an exact width and height, the photo can get squashed. Resizing by the long edge with the ratio kept is the safe choice.

iPhone HEIC photos can't be opened in the image resizer. Set the camera to "Most Compatible" or export the photo as JPEG when you share it, then shrink that copy.

Step by step

  1. Check what the site asks for: the maximum file size, the pixel size and the accepted formats.
  2. Upload the photo to the image resizer; its resolution, format and file size appear right away.
  3. Set the size by the long edge or by percent. The resulting pixel size is shown before you run it.
  4. For a photo, choose JPEG or WebP and set a quality. Starting at the default of 85 works well.
  5. Run it, compare the file size before and after, and if it is still too big, lower the size or quality a little and run it again before you download.

Frequently asked questions

Can it hit an exact file size, such as 500 KB?

No. There is no setting that aims for a target file size. Each run shows the original and result file sizes, so adjust the size and quality a step at a time until the file fits the limit.

How small can I go and still keep it looking good?

For photos seen on a screen, 1,600–2,000 px on the long edge at JPEG quality 80–85 usually looks the same. If the photo will be printed, it is better not to shrink it.

Is my photo stored?

No. It is sent to our server to be resized and is not stored.

Can I shrink several photos at once?

The image resizer works on one image at a time. If you need to hand in several photos as one file, see the guide to putting photos into one PDF.

Tools used in this guide