[font color=\'#000000\']An 8x10 print is measured at it's outer border. It can be printed in a variety of ways, and matted in even more ways.
For example, I might print the 8x10 with a quarter-inch border on all sides, mount that to a backing board, then cut an overmat that is exactly 8x10. Or the overmat might be even larger to expose the entire print with a quarter inch of backboard showing. Or I could print the 8x10 all the way to the edge, and overmat it so that the mat covers the outer quarter inch of the print. Or I could cut an overmat to only expose a panoramic portion of the 8x10.
There is no standard other than the framer's good taste.
Standard print sizes now come in two variety: wet lab sized and digital print sized. Wet lab sizes are those you can get from the paper manufacturer, typically (in inches), 8x10, 11x14, 16x20, 20x24, all roughly fitting the 4:5 radio of most film formats (square frames of 2 1/4" film and elongated frames of 35mm film being the exceptions). Larger material comes in rolls that are cut after printing and developing.
Digital print sizes tend to match the standard paper sizes: 8.5x11, 13x19, the European A sizes, and in 17", 24", 36", and 44" rolls for larger work.[/font]