"Save as" from PSD to jpeg creating very small files

[kennyk77]

When I try to "save as" in photoshop (document size 14x14 in 300 res 33mg) to jpeg quality 12 the size is reduced to kb or maybe a 1 mg or 2.  Not understanding why the jpg size is not bigger.  Am I missing a step?  These are mainly composites.  Regular files save with larger mgs.  I need to save as jpg to send to lab.

Kenny

[Mohammad.Harb]

which measurement units are you using? cm or inches or pixesl! 
what do you mean exactly  by "send it to lab " 

[kennyk77]

Using inches.  "send to lab" means uploading to my lab for printing.

[Mohammad.Harb]

Why not considering Tiff format?

[kennyk77]

Photo lab only accepts jpg files.

[Ko.Maruyama]

"Save As" should only change the document format.

If you are using "Save for Web (Legacy)" or "Export As", you have options to change the image size during the conversion.
Make sure that you're still using "Inches" in the dialogue box - the default may be "Pixels".  The values should automatically scale to the translated dimensions, but it's possible that they are adopting a preset or previous document's unit settings.

If the image looks ok, but the file size is just unexpectedly smaller, it's possible that there is lots of Metadata attached to your photoshop file. Depending on the file, metadata can account for several Mb of information.  Saving it as a different format can strip out the information (camera info, history, notes) that doesn't effect the image display.

I would recommend that you ask your lab if they can accept other formats for future deliveries.

[kennyk77]

YOu can see the original size is 15mg but after "save as maximum size" it ends up less than a mg.  This only seems to happen with my composites.  Regular photos "save as" produce a reasonable size.

[Per Berntsen]

The file size of a jpg is determined by pixel dimensions and quality setting, but also, to a large extent, by image content.

Images with lots of busy, sharp detail (or noise) do not compress well, and will have a relatively large file size.

Images with large, flat and/or out of focus areas do compress well, and will have a relatively small file size.

The difference in file size can be quite dramatic.

The two images below have the same pixel dimensions, and have been saved with the same quality setting.

40 kb

145 kb