Printer specifications are real and accurate and meaningful, but are not to be confused with image resolution. Printer ink dots and image pixels are simply very different things, and one color image pixel requires many printer ink dots. This is why we need a 1200 dpi printer (ink dots) to print an image at 250 dpi (pixels).
Q: What are the standard postcard sizes you offer? A: For flat standard postcards, available sizes are as follows: 4 x 6, 4.25 x 6, 5 x 7, 5.5 x 8.5, 6 x 9, and 6 x 11. Folded postcards have 2 kinds: half-folds and tri-folds.
If you want to qualify for the First Class postcard rate, your mailing must be: 1  A rectangle. 2  At least 3.5 inches high by 5 inches long by .007 inches thick. 3  No more than 4.25 inches high by 6 inches long by .016 inches thick.