A USPS Flat Rate Box offers one low flat rate, so pricing is determined by the size box you choose rather than the weight of the box or the destination of the package.
Priority Mail Flat Rate is a shipping service offered by the United States Postal Service (USPS). The service allows a maximum weight of 70 lbs. Priority Mail Flat Rate includes free shipping supplies available at a local post office or sent to your home or business at no extra charge. Postage may be purchased at a post office or online at USPS.com. Once your package is ready for shipping, you can schedule free pickup from your home or office.