An imported 4x3 jpg does not match the aspect ratio of the 4x3 marquee tool. Why?

[Myphototrail]

For example - see attached photo...I import a jpeg photo into photoshop with a 3x4 aspect ratio (900x1200).

I use the rectangular marquee tool to draw a frame box around the photo, set to fixed 3x4 aspect ratio.

I would expect the box to be the same aspect as image.  But the box is always visibly taller...by about 10%.

When I check the info on each object...the pixel count indicate they are both indeed 3x4.  But they don't match up visually.

Can anyone explain this frustrating problem?

[D Fosse]

The explanation is in fact in the aspect ratio. A fixed percentage isn't the same width on the two axes.

Think of it this way: keep adding the same width on all sides, and you get closer and closer to a square.

[Myphototrail]

Thanks for reply...but I'm still unclear.  If I compare the number of pixels:

jpg:  900x1200, box:  2050x2733 

Both are 3x4 in pixels.  Yet the box appears taller.  So, does this mean the pixels of the box are stretched?

How is it possible to create a 3x4 box then?

[D Fosse]

No, the pixels aren't stretched. Set the rectangular marquee to "fixed ratio" at 4:3, and just try for yourself.

Again, it's because the long side has more pixels, so a percentage increase adds more pixels on the long side than the short side. The border gets wider.

If you want an even width border, you don't get the same aspect ratio. As you keep adding, the rectangle becomes more and more square.

This is just the way geometry works. Both these are 4:3, just measure them if you wish:

[Myphototrail]

Sorry....I don't get it.  I am setting the marquee tool to fixed.  Simply trying to create a 4x3 frame that matches a 4x3 jpg. Thanks.   I give up.