How can I set DPI for a document in illustrator?

I couldn't disagree with the accepted answer more.  You have a lot of authority, telling the entire world of designers what's "Inappropriate" for a user who simply want to be able to see a ruler in the emulated DPI of their own intended context.  You suddenly know the use case of every designer in the world enough to just tell people what is or isn't possible or appropriate?  That's ridiculous, this use case is common sense and has been needed for YEARS, and I only know this because this issue is now is causing one of my client's quite a lot of trouble trying to simply open an SVG that has a pixel size intended for 600dpi and seeing nothing even close to the mm size in Illustrator.  And yet, our own home grown software does this JUST FINE. 

Think about this:  Photoshop has the feature to set the DPI, change the rulers automatically, and it's incredibly useful to the professionals who use it.  Ilustrator is like the sister of Photoshop, very similar, made by the same company, has a painfully similar UI structure without actually feature matching, and thus people's expectations are already set by this.  So, this shouldn't be a surprise request, since the common use case on the PS side was created by the same company, it's natural to expect consistent features or usability in the sister software, even if one is vector, and one is raster.

User Feedback is Clear

So, seeing that users have expressed CLEARLY that they simply want a useful feature that shows a ruler and the artboard size in a way they can control for their own reference, let's also point out that it can be entirely unobtrusive - that is, it doesn't have to be the default, it doesn't have to be enabled out of the box, everything can remain the same in Illustrator if you don't use the added feature.  But, for those of use who LEGITIMATELY NEED THIS, if it was there, it would be helpful to professionals who rely on the software for similar features.  There's nothing "inappropriate" about that.  The most inappropriate thing in this forum thread is anyone saying to someone else that "YOU DON'T NEED THAT" when you don't know what they need, because you're not them, and they actually have an honest, legitimate use case that resonates with thousands of other power users.

Nobody Cares About How Well You Understand the Definition of Vector, and Adobe Has Already Exceeded It

Now, as you get tripped up entirely on some evangelical explanation of vector, just stop.  That's not the point, we all get it, idealistically forcing vector down people's throats is what the norm is Today.  The thing is, for professionals relying on the software, that sucks.  Thus, nobody cares about the norm, nobody needs 5 explanations of the same runaround, of what true vector is or isn't, because good innovation is what they expect from Adobe when it's simple forms like this.  Not lessons on being a tight ass for semantics.

Illustrator is vector?  Great.  Let's make it more than that with simple helpful features like they ALREADY have done!  That's not inappropriate, that's good product development and finishing what they've started.

Adobe Already Converts to Units of Measure with 72DPI Even Though All Monitors Do Not Have This Resolution!

As a software developer, and graphic designer, and developer of graphic design apps, it's clear to see Adobe has ALREADY implemented a conversion of vector to DPI by offering an ArtBoard size and a Ruler that has real world units of measure in the first place, so that "arbitrary" conversion has already been hard coded to what only fits the primary use case.  Believe it or not, there is more than one valid use case for the definitive vector editing software of the world, and that's not anyone's right to decide for everyone else, because it's about needs and innovation of the future as we create it, not old standards that you're stuck on. 

Trying to point out that "VECTOR HAS NO UNIT", that pixels are color codes, that units of measures are simply ratio conversions, blah blah is just ignorant because this exact concept is already there in AI and PS, just not in AI in any way that's as versatile and it doesn't actually update to match the monitor, so it's not even doing real screen size units.  So, almost nothing people are pointing out about "how it should be" is even valid, because it should at LEAST be accurate to the monitor, if that's why "72ppi" was hard coded one fateful day in the early 2000s or late 90s or whenever this was decided by one release to be the end all be all of ruler units and artboard size labels.

72dpi should not be hard-coded for everyone when that's not accurate on every screen, since screens come in all types of resolutions now, including 72, 96, 100, and higher with Retina and other 2x and 3x resolution displays, etc.  This feature was only valid when all screens had the same resolution, so an update here is already necessary.

SIMPLE FEATURE REQUEST TO COPY PHOTOSHOP WOULD SOLVE EVERYTHING

So, I humbly request that everyone get off their high horse, and accept a simple but highly useful feature request that helps people bridge the gap between Vector and real world units of measure, with two parts:

1) Artboard properties > size area option to change DPI / emulated resolution from default 72 to variable within some practical range (1 - 1000?).  A button to pop up a editing dialogue for this value complete with resample checkbox (like photoshop)

2) Ruler changes scale to match artboard resolution

Ex:  see Photoshop, where you've set people's expectations for this functionality already.

If you absolutely hate it, just make a setting in preferences that turns it on and otherwise hide it entirely like it is today.  A preference like " Show DPI Settings yes[ ]  no " is all it would need to be, to toggle #1, and you can have a little warning there that links users to this forum to learn all about the nuances of vector, for those who care.

Byproduct of this is basically a bug fix for the rulers since users can then set the artboard / document resolution to match their monitors if they have high-def monitors, as anyone with a modern mac or HD monitor has now, to fix the currently broken rulers for those users.

Seems not just valid and incredibly appropriate, but also pretty overdue to me.

I've been looking for a way to set my Ai document resolution. I found this discussion.

Indeed, from the programmer/mathematicians perspective, a vector program don't need a logic unit system, because vectors don't have units, by definition.

But the users of this application are mostly designers who deal with unit systems (pixels for the web, cm/mm for print, and often a combination of both).

In my case, the medium I am working on right now is a specific display. This display has a size in pixels, and in mm, and of course a resolution. I definitely need to be able to set my graphics sizes both in mm and in pixels.

Again, the application's usability should not reflect the maths behind the programming, but what the users really need. It's as simple as this (otherwise we would still be using MS-DOS).

Please Adobe, allow your buyers/users/customers/stakeholders to set units and resolutions in Illustrator.

Thanks

Whaddayaknow. HEY ADOBE: Maybe if almost 10k have viewed this page, maybe this something important to consider! Maybe you should get the elitism stick out of your butts and realize that people have a need for a global DPI setting for their document.

Here is my case, masters of Adobe, and you tell me if I am just clueless and retarded, or if what I am saying makes sense:

I am making an envelope. A simple #9 envelope! However, when I went to set the appropriate size in INCHES when creating a new document, it ROUNDED THEM OFF TO THE NEAREST TWO DECIMAL POINTS. How dare you!!! Turns out IL did this because the native resolution of the doc is 72ppi - and that's that. So when I create a new doc in inches, it's forced to round that off because 8.875" in 72 PPI is like a few hundred measly pixels with a decimal point. I don't want a doc that's 8.88", I want 8.875" exactly!!!

OK, I thought to myself. I will just create a document in pixel dimensions that will equal 8.875x3.875 @ 300ppi. Yay, it's all relative, right? Once I set my pixel dimensions (yes, I get it, they are not actually pixels, it's all arbitrary, etc.), I want to be able to export a file that is scaleable to whatever DPI will yield me a PDF with the EXACT dimensions I need. Not 2-decimal round-offs. So this should be possible! NOPE. No PDF option in the exports, "save as" yields me the usual PDF window which makes no mention of what the actual print dimensions of the document will be. There is literally nowhere to adjust the size of the thing, and unless I decide to use another program, I cannot rescale my document to a different inch size without conforming to their stupid 72 dpi limitation.

So let us say that I want to produce, in Illustrator, an image that, when exported, will measure some several thousand (actual) pixels in height & width. I don't care about sizing of the elements within this file, so I don't need to know that some little image is 36x36 actual pixels instead of 100x100 point pixels. Let us say now that I want this image to be saved as a document of particular print dimensions of my choosing - for example, I have a high-resolution 10k x 10k pixel image I want to export as a PDF that will print at 1x1 inches on a card. I WANT TO DO THIS WITHOUT LEAVING ILLUSTRATOR.

Adobe, are you really telling me this is not possible??? What am I failing to consider??

Drawing programs like Illusrator are object based. An Illustrator file can contain any combination of scaleable vector paths (its main reason for existence), text objects, and raster images.

Because those elements are each separate objects, there is no "pixel" count that actually means anything at the whole document or whole Artboard level. Illustrator's rulers are for actual measures, and a pixel is not a unit of actual measure. A pixel can be any measure.

You can set an Illustrator Artboard to 1024x768 "pixels" according to its misleading rulers all day long, but that really means nothing other than that the Artboard size measures 1024 x 768 points (which is an actual unit of linear measure).

If you then draw a vector path on that Artboard, the rulers may tell you it's "size" is 50 x 100 "pixels." But that is nonsense, since by definition there are no pixels in that vector object. The object is merely scaled to measure 50 x 100 points.

You can then set some text on that same Artboard. the rulers may tell you the text height is 24 "pixels." Again that is nonsense, since there are no pixels in that text. Text glyphs are vector paths. The vector paths are merely scaled to measure 24 points.

You can then import a raster image onto that same Artboard. The rulers may tell you the "size" of that raster image is 50 x 100 "pixels." Even now, that means nothing more than that the raster image is scaled on the page to the size of 50 x 100 points. That image could contain any number of pixels. For example, it may contain 500 x 1000 pixels in which case its PPI would be a ridiculous 720.  They'd all just be scaled down to a much higher per-inch count than the 72 PPI which Illustrator arbitrarily considers "100%."

Or, that image may contain only 25 x 50 pixels, in which case its PPI would be 36.

Moreover, there's nothing preventing your having both of those images onto the same Artboard at the same time. The rulers would tell you they both measure 50 x 100 "pixels". You can see that is nonsense. They each are merely scaled to measure 50 x 100 points, and that has nothing whatsoever to do with how many pixels they contain.

But now suppose you export that file to a raster format. When you do that, everything on the Artboard—vector paths, text objects, and raster images—gets rasterized (or re-rasterized, i.e.; resampled in the case of raster images) to whatever number of pixels you specify in the export dialog, regardless of whether that's the so-called "Save For Web" dialog, or the more straightforward Export dialog. That's the only place that a document-wide "PPI" or number of pixels means anything, because you are now rasterizing the entire stack of individual objects to a single raster image.

So don't even look for a "document PPI" or an "artboard PPI" or a document "V-pixels-by-H-pixels" count. There is none. This is an object-based vector (scaleable) program. The "Pixels" unit-of-non-measure is bogus. It's merely an interface "convenience" for those who want to think in terms of pixels, even when it's inappropriate to do so.

As is made so obvious by the frequency of repetition of this very question in this fourm, that silly interface creates more confusion than convenience.

JET

Illuststrator displays at 72ppi and  and the measurements are actually based on points. The raster effects settingoly affects the translation of the effect not the documennt.

You ahould simply work in pixels and not concern yourself with cm.

Then save for web and device were you can set the image size.