How to add transparent padding of fixed number of pixels to an element?

Question

I do not want initial image to change size, I simply want to add transparent padding around what I already have.

Answer 1

To increase by an exact, specific number of pixels, I'd do this:

1. First double check that Illy is thinking in pixels. View > Show Rulers (if they're not shown already) then right click on the ruler and select pixels.
2. Use the Artboards tool in the tool palette, select the main artboard you want to change
3. Double click on the artboard tool icon in the tools palette where you selected it. A properties window will pop up, with width and height in pixels (or whatever the ruler is set to)
4. Type in the new values you want, or, use the up arrow (and down arrow) in each field until you have the padding you want. In CS6 (and also earlier versions, I think) it updates automatically on the page behind you, so you can check it looks how you want.
5. If you don't want the same padding on each side, use the "reference point" icon to select which side you want to be fixed

This changes the artboard (the canvas) without touching the images inside it, letting you add (or remove, or move) by the exact number of pixels you want.

Answer 2

Change the canvas size. I would go through Photoshop though.

Answer 3

Draw a rectangle the size you want. Set it to have no fill and no stroke. Align your art to that rectangle. (it may be easier to give it a stroke until things are aligned, then remove the stroke to save/export)

From there, you can either convert it to an artboard (Object > Artboards > Convert to Artboard) if you are using CS4+ or you can just leave the rectangle and exporting/Save for Web will see that as the artwork boundaries.