What size should an image be for email?
Two numbers matter and people mix them up: the pixel dimensions, which decide how sharp it looks, and the file size, which decides whether it sends.
The limits you are actually up against
| Service | Attachment limit | Note |
|---|---|---|
| Gmail | 25 MB total per message | Larger files are swapped for a Google Drive link automatically. |
| Outlook.com | 20 MB per message | Desktop Outlook against Exchange often stops at 20 MB too. |
| iCloud Mail | 20 MB per message | Mail Drop takes over above that for Apple Mail users. |
| Corporate mail servers | Frequently 10 MB | The receiving server's limit applies, not just yours. |
Two traps hide in that table. First, the limit applies to the whole message, so eight photos share one budget. Second, attachments are MIME-encoded in transit, which inflates them by roughly a third — a 20 MB pile of photos can be refused by a 25 MB limit. Aim for about two-thirds of the stated cap.
And the practical limit is lower than the technical one. A 24 MB email is a rude email: it is slow on a phone, and it sits in the recipient's mailbox forever. Under 5 MB per message is a good target for anything routine.
Pixel dimensions that still look right
| Purpose | Long edge | Typical JPG size at quality 80 |
|---|---|---|
| Inline in the message body | 800–1000 px | Usually a few hundred KB |
| Viewing full screen on a laptop | 1600–2000 px | Around 0.5–1 MB |
| Recipient will print at 6×4 in | 1800 px (300 dpi) | Around 1 MB |
| Recipient will edit or print large | Send the original | Use a file-sharing link instead |
Sizes in the last column depend on the content — a busy landscape carries far more detail than a portrait against a plain wall — so treat them as the order of magnitude, not a promise.
The order of operations
- Resize first. Reducing a 4000 px photo to 1600 px removes 84% of the pixels. No compression setting comes close to that saving. Resize the image.
- Then compress. At the new dimensions, quality 80 is usually indistinguishable from the original at arm's length. Compress the image.
- Send JPG, not WebP. This is the one place where the older format wins: recipients may open the attachment in decade-old desktop software that has never heard of WebP.
- Strip the metadata if the recipient is not family. Phone photos carry GPS coordinates and a device serial in their EXIF block. Remove EXIF data.
Hitting an exact ceiling
If the limit is hard — a form that rejects anything over 100 KB, or a mail server that bounces at 10 MB — work backwards from the target rather than guessing at the quality slider. The compress to a target size tool searches the quality range for you and stops at the largest file that still fits under the number you set.
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