Why do PS, Mail.app and the Finder all give different jpeg file size

[thermarest]

One recent example:

Photoshop estimates a 132kb file in the Save As dialog
Finder sees it as 216kb after saving
Mail.app calls it 184kb

usually if I view an attachment in the Yahoo mail web interface it gives yet another value.

If these were off by a few % it wouldn't puzzle me, but 75%?

Mostly I'm just curious, but once in a while when there is some strict limit to an upload size, this is rather annoying.

[M A V I C]

I just gave it a try.

PS save for web: 19.36KB (note that B is Byte and b is bit)
Finder: 20KB (20,096B [= 19.36KB])
Mail.app: 32KB

So here's the deal, PS gives the actual file size. The Finder gives it based on the number of blocks it takes up. Get Info shows the real size as well, which matches PS. Mail.app gives the message size, so that's probably the size it takes up in blocks as well as the size of the message too.

[Jimmypoo]

and/or any enclosure that Mail must wrap the jpg in, so that it gets through.

But I agree, it's probably mostly the html to attach the file, unless you use Mail.app
strictly in plain-text. And even that has to have SOME size.

[JoeH]

Standard B64 mime encoding will cause an attachment to be about 1/3 to 1/2 larger. That is the size Mail is reporting, as that is what will trigger size limits on email servers.

[thermarest]

Cool. Thanks for the answers.