Adobe Illustrator pixel to mm formula?


I import VECTORS in illustrator that i want to lasercut but they are measured in pixels. I want to output that to DXF. However i am wondering if pixels are converted to mm using a standard formula in Illustrator.

From what i am guessing however Illustrator is set to default DPI at 72 so the formula is standard (pixels*25.4)/dpi. Is this correct? Also is this the standard that Illustrator uses?

If i take this and reverse it i can see that illustrator multiplies the pixels by 2.8347. If i always scale the pixels using 283.47% will i always get the same result in mm? Is there anyway this can go wrong or is it hardwired and non-changeable in Illustrator?

Thank you


12/5/2012 7:47:00 PM

Illustrator doesn't measure anything in pixels primarily because Illustrator, being vector-based, is math-based and a pixel has no size.

Illustrator has no "default [PPI]" because it's a vector-based, resolution-independent, application. The only time PPI is used within Illustrator is when placing raster images - in which case the image PPI is used, or creating raster effects - in which case the settings under Effect > Document Raster Effects Settings are used.

Illustrator essentially uses 1 point to equal 1 pixel for measurements. While this is not really accurate and pixels can easily vary in size, this is done to preserve at least some logic in the application. Again, because you can't measure a pixel. You'd be better served with a point to millimeter conversion. This is also where you've "guessed" at Illustrator using 72ppi. It's not, it's using points and there are 72 points to an inch. Or 2.834645669 points to a millimeter. That formula which was posted, while accurate for points is completely *inaccurate* if referring to pixels.

You can't think of pixels as having a size. They do not. So to answer your question.... no. Because there's no way of determining the size of a pixel without also knowing the width and height of the entire image, as well as the total number of pixels contained in the image.

12/5/2012 8:53:00 PM