How to compress images for email attachments

A photo straight from a phone is often several megabytes, and a handful of them can push an email past the size limit, so the message bounces back or refuses to send. The fix takes about a minute per photo: check the size, resize it to a sensible width, compress it, and attach the smaller copy while keeping the original untouched. Everything below runs in your browser on ImageTool.us — your photos are never uploaded anywhere.

Why email rejects large images

Most email providers cap the total size of a single message, including all attachments, at roughly 20 to 25 megabytes, and the exact limit varies by provider and by the recipient's provider. A message with five uncompressed phone photos can easily pass that cap, and the sender usually finds out only from a bounce message. Compressing first also helps the recipient: a smaller attachment downloads faster and takes less space in their inbox. If you are unsure of your provider's exact limit, treat 20 megabytes for the whole message as a safe working ceiling and aim well under it.

What size should you aim for?

• One or two photos in an email — under 1 MB each is comfortable.
• Several photos in one email — aim for about 200 to 500 KB each, so the total stays well under the cap.
• A photo that will only be viewed on screen — a width of around 1600 pixels is plenty; nobody needs a 4000-pixel-wide file inside an email.
• A photo the recipient needs to print — keep it larger, but still compress it once from the original rather than sending the raw file.

Step 1: Check the size before you attach

On a phone, open the photo's details to see its file size; on a computer, right-click the file and check its properties. If a single photo is already over 1 MB, or the set of photos together is over about 10 MB, compress before attaching. This one check prevents most bounce-backs.

Step 2: Resize to the width you actually need

Resizing is the biggest single saving, because a 4000-pixel-wide photo shown at email width wastes most of its pixels. Use the Image Resizer to bring a photo down to around 1600 pixels wide for on-screen viewing, or to an exact size such as 1920 x 1080 if the recipient needs a larger version. Resize first, then compress — compressing a full-size photo and resizing later means doing the work twice.

Step 3: Compress to a target size

After resizing, compress the copy. The Image Compressor lets you pick a quality level, and if you want an exact result, the target-size tools do the guessing for you: Compress Image to 200KB and Compress Image to 100KB shrink the photo until it fits the target, or get as close as the image allows. For how far you can lower quality before the loss becomes visible, see the guide to compressing images without losing quality. If a photo is already under your target, the tool says so and leaves the original file untouched instead of re-encoding it into a larger file.

Step 4: Convert the format if it helps

Photos saved as PNG are much larger than the same photo as JPG, with no visible benefit when there is no transparency involved. If a photo attachment is a PNG, convert it with the PNG to JPG Converter before compressing. For the full reasoning, see the guide to the best image format and the JPG vs PNG vs WebP guide — the same format rules that speed up a website also shrink an email attachment.

Step 5: Attach the compressed copy, keep the original

Always compress a copy and keep the original file as it came from the camera. Compression removes data that cannot be recovered, and if the recipient later needs a print-quality version, you will be glad the original still exists. Attach the compressed copy, send a quick test to yourself if the message is important, and only then delete the working copy if you need the space.

Common mistakes

• Attaching full-size phone photos and hoping the message goes through.
• Zipping photos to shrink them — a ZIP file barely shrinks a JPG or PNG, because those formats are already compressed.
• Compressing after attaching — the attached file is a copy, so editing it in an editor does not change what is already attached.
• Shrinking a photo so far it becomes unreadable — a document photo or a screenshot with text needs enough resolution to read.
• Re-saving a JPG many times — each save loses a little quality, so compress once, from the original.
• Sending a PNG photo when a JPG would be a fraction of the size.

Quick checklist

• Checked the total size of all attachments before sending.
• Resized photos to around 1600 pixels wide for on-screen viewing.
• Compressed each photo to under 1 MB, or about 200 to 500 KB for multi-photo emails.
• Converted PNG photos to JPG where transparency was not needed.
• Attached the compressed copy and kept the original file.

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