coverting between K and dpi

[regan]

i'm trying to submit an image to a magazine that wants 72dpi. the export in lightroom says K.
how do these compare. how many dpi are in a K or are they equal?

 

[Ido]

These are two completely different things.
The 'K' is in File Settings, and stands for 'kilobytes'. If you check the box next to it and type, say, 4096 in the box, then the compression Lightroom uses to export will be the lowest it can go (so best quality possible) while keeping the file size at or under 4096 kilobytes (4 megabytes).
To set the dpi, just go further down to Image Sizing, then next to 'Resolution:' type 72 in the box, and make sure that 'pixels per inch' is selected in the drop-down menu.

By the way, that dpi setting means absolutely nothing, if you don't tell Lightroom to resize the photo to a specific canvas size (inches, not pixels). I'm really surprised that the magazine even requests that.

 

[KmH]

There are 3 considerations:
File size - which is usually in Kb (kilobytes) or Mb (megabytes).
Image resolution - the pixel dimensions of the photo (3265 x 2546 pixels)
Print resolution - how many ppi (pixels per inch)

The magazine didn't even use the right term for print resolution because it's ppi, not dpi.
For electronic display there is no need to set a print resolution since a print is not being made.

Photoshop Help | Image size and resolution

 

[TCampbell]

dpi and ppi are meaningless unless they also includes at least one other value... either the image dimensions in pixels or the image dimensions in some unit of measure (such as inches).

If I am producing a print magazine and I intend to give the image 4x6" worth of space on the page but I intend to print at 72dpi... then I could tell you I need 72ppi for a 4x6" and this would tell you that the image needs to be resampled to 288 x 432 pixels. That's because 72 x 4 = 288 and 72 x 6 = 432. You can do something with that much information because you can actually resample the image and set the ppi. By doing so, the image will render at exactly the size they want on the page.

Suppose they want to do a 4x6" and they've got an image which is (I'll just use round numbers to make the math easy) a 2000x3000 pixel image. You could divide 2000 ÷ 4 = 500 (also 3000 ÷ 6 = 500). That would tell you that if you set the image to 500 ppi then you'd get the image size you want without needing to resample the image to different resolution.

But when all they do is say "we want 72 dpi" ... that doesn't mean anything (except that the person relaying the request doesn't understand how it works.)

 

[KmH]

Dots per inch - dpi only applies to output devices.

The most basic inkjet printers have to use 3 dots to print 1 pixel - some combination of cyan, magenta, and yellow CMY.
Home printers use 4 colors bt adding black - CMYK. The black made by combining just CMY isn't all that black.

High quality inkjet printers use up to 12 colors and hence use more dots to print a pixel and have print heads that produce up to 175 dots per print head.
So to print a photo having a print resolution assignment of 300 ppi, high quality inkjet printers may print 9600 dpi to print the 300 pixels in an inch of print.