Is there a way in Illustrator to know the exact dimension of shape in pixel and possibly to resize it down to different (but precise) dimension?
If you got multiple objects that you want to resize as one, you need to start by selecting all of those objects with the Selection tool.
Still with the Selection tool, in the upper right corner you will see the width and height boxes that you can use to resize your objects.
Alternatively you will find the same boxes from the top menu:
Window > Transform
If you want to keep aspect ratio, you need to click the chain between the boxes.
Good answer, No grouping needed though. Just select object the control bar will read the width and height of the selected object whether it is 1, 2, or 100.– ScottAug 30, 2012 at 22:39
Thanks for your answer, actually (at least in my version of Illustrator, the box you mention is under the "Transformation" menu in the Control bar Aug 31, 2012 at 5:35
Whether or not the fields are there actually on the control bar or under the transform link on the control bar all depends upon your screen resolution.– ScottAug 31, 2012 at 6:56
@Scott: Yea, you are right :/ There is no need for grouping. Edited my answer. Silli: Yes, I usually add the top menu alternative to my answers because those area always there and they may be easier to find. Added that into my answer as well. Toolbar on the other hand might not be in it's usual form due to your resolution as scott mentioned.– JoonasAug 31, 2012 at 7:31
The simple way is to select the object that you want to resize and then the transform option where you can enter precise dimensions for your object.
I just wanted to expand on some of the answers already given here. The Height and Width details in the Properties window make this possible (use Window > Properties) if it isn't displayed in your panel to the right.
Once you use "File > Place" to place the image you'd like to work with, you can use the Direct Selection Tool (A) to select it. With it selected, the Properties window changes to give you the exact dimensions of the image. You'll see this in the "W:" and "H:" sections of the window. (See attached.)
Follow the advice in Joonas' answer, but also keep in mind that the pixel dimensions that show up in the control bar will only be accurate when you export at a resolution of 72 ppi. Except when you have a raster image in your Illustrator layout, pixels don't actually exist. What you see on screen is an on-the-fly rendering of the vector art, based on the resolution of your monitor. Those "pixel dimensions" Illustrator gives you are based on its fixed and definite idea that 1 pixel = 1 point. If you export a "500 pixel" wide object at a setting of 300 ppi, the jpeg or png will be over 2,000 pixels wide.
I've not tested how this effects alignment to the pixel grid, but I'm not optimistic that it would necessarily be retained on export at anything other than 72 ppi. Scott may know the answer to that one.
Also, Photoshop can give you the image's dimensions and resolution even before you hit Illustrator.
In Photoshop, with the image opened, use Image > Image Size to get a dimension reading to help you when creating a new file in Illustrator.