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.
The U.S. Postal Service allows customers to use the postcard rate for First-Class Mail for postcards that are at least 3.5 inches high by 5 inches wide but no more than 4.25 inches wide by 6 inches wide. As of April 2014, the postage rate for a postcard of this size is 34 cents. USPS also has a First-Class rate for large postcards that are no more than 6.125 inches high by 11.5 inches wide by 0.25 inches thick. These postcards cost 49 cents to mail as of April 2014. Learn more about Postal Services