I'm trying to increase the PPI of my logo using Adobe Illustrator, but when I export it the image dimensions that should be 131x31 increase to 268×64. How can I fix it?
It's good to remember that as far as Creative Suite vector applications are concerned, 1 pixel = 1/72nd of an inch (1 point). If your image is 500x50 points (or even 500x50 pixels!) wide in Illustrator, it will export at that pixel dimension only if you export at 72 ppi.
If you need a higher resolution version at the same printed output dimensions, then after you have exported the image, take it into Photoshop and change the dimensions to what you want using
Image > Image Size. Be sure to uncheck "Resample Image" in the dialog.
You tagged this question
website-design. If this is truly what you want to do with the image, you should not be concerned with ppi at all. It is a meaningless value when applied to a web image. See this discussion for details of the difference between ppi and dpi, and this one related to web images.