Applicability of the New Rules. The new cargo securement rules apply to the same types of vehicles and cargo as the old rules, covering all cargo-carrying commercial motor vehicles (as defined in 49 CFR 390.5) operated in interstate commerce.
Most commercially-produced postcards measure approximately 4.21 inches by 5.47 inches. Less commonly, smaller postcards are typically 3.5 inches by 5.5 inches, close to the minimum size the USPS allows.
As of Jan `014 large postcards rose 3 cents to $0.49, up from $0.46 to mail. These have maximum dimensions of 11 1/2 x 6 1/8 and can measure up to 1/4 thick. Postcards are a great way to save over the price of first class letters.