I am often asked how many pictures (or documents) can be attached to a single email. The answer: it’s not how many, it’s how big.
Each email service provider limits the size of any one email you can send (typically 25 megabytes); the smaller the pictures, the more of them you can attach to a single email.
Pictures generally range in size from small (150 kilobytes) to large (1 megabyte, or 1024 kilobytes). Thus, you can attach up to roughly 15 large images — or many more smaller images — to any one email. (In addition to attachments, the overall size limit of the email includes the room taken up by text, formatting and signatures).
How do I know what size my pictures are and whether I’ve reached the limit?
In most email programs, the size of the file is displayed when you attach a picture; as you attach more pictures, each file size — or the cumulative file size — is noted.
Can I change the size once I determine what it is?
Yes. If you wish to reduce the size of an image, you can detach it from the email and open it in a photo editing program. Or, if your email program allows, you can change the size of the attachment within the email itself. Some mobile devices will ask you if you wish to send the attachment as a “small,” “medium,” or “large” file size.
Note that image size is not just the dimensions, it is also the number of “dots per inch” (dpi). Reducing the size of an image does not necessarily mean cropping out some of the content (although that will certainly reduce the file size), it means changing the overall proportions of the image in conjunction with reducing the number of dpi.
Shouldn’t I just always send the smallest size so I can attach more pictures and reduce the upload and download times?
No. There are reasons to send large images and reasons to send smaller ones. Determine which to send by how you think the recipient will use the image(s).
If you send your friends a few pictures from your vacation or you send your insurance agent some pictures of the dent in your car, you need only send small images; the recipients are likely to only view the images on their computer screens. If however, you are sending a picture that might be printed in a book, a program, or a brochure, for example, you should send a larger image. Print images need to be about 300 dpi to be really crisp, compared to screen images that need only be 72dpi.
Of course if you find yourself up against the file size limit of a email, just send more emails, each with fewer attachments.