In the Export Bitmap dialog, there is a Custom option, where you can set your own dimensions, if the Page, Selection, or Drawing options aren't right for you. If you set page dimensions in Doc Props, then export with the Page option, the new PNG file will be the same as what you set in Doc Prop.
If you do that, but don't see your image in the resulting PNG, it's probably because your image is not inside the page borders. Also in Doc Prop, you can enable or disable the page border. If you disable it, you have no idea whether your image is within the border or not. So if you prefer to draw with the border disabled, it's important to use "Resize Page to Content", which moves the page border to exactly fit your image. You can, as of 0.48.0, add margins as well. (In previous versions, it's called "Fit Page to Selection" with no margin options.)
It's always very important to check that the dimensions are what you want, before performing the export. That's because sometimes the options you used the last time are still showing in the dialog, and might not be appropriate for your current needs.
Well, I guess it's not so easy.... Thank you anyway, but in the meantime I've been searching for answers and I found this in relation to "Export Bitmap"- I must say I totally agree with point 5 when he says "Why can't the units of these measurements be changed?" This option shouldn't be so fixed.
http://wiki.inkscape.org/wiki/index.php ... ort_Bitmap
In the Export Area portion of the Export Bitmap dialog, it IS possible to use any units you want. In the Bitmap Size portion of the dialog, I think it must say only "pixels", becase DPI means "dots per inch". And dots on the screen are equal to pixels. It is the bitmap (or raster) size. But as long as you have selected the proper export option, and checked that the dimensions and units are proper for your drawing, and you have used "Resize page to content", the export will be the size you intend, even though it is expressed in pixels. In other words, just because it says "pixels" it doesn't change the size of your export.
(Who is Andrew? Personally, I think the Export Bitmap dialog is fine, except for its name. I would like it to be called Export to Raster Formats, or Export Raster.)
So I hope that clears it up some for you. Let us know if you have further questions
