The US Postal Services have flat rates for different sizes of packages and boxes. The USPS has fixed prices for boxes for all sizes. You can send any box of any size and get a flat rate. But, the USPS has dimension limits for your box to fall into either one of the size categories. The different sizes are as follows.
- Small Flat Rate Box
- Medium Flat Rate Box, top loading
- Medium Flat Rate Box, side loading
- Large Flat Rate Box
- APO, FPO, DPO Flat Rate Box
- Large Flat Rate Board Game Box
Here are the dimensions for different sizes available for flat rate boxes as well as the shipping price.
| Size | Dimensions | Price |
|---|---|---|
| Small Flat Rate Box | 8 11/16″ x 5 7/16″ x 1 3/4″ | $7.90 Commercial Base $8.45 at Post Office & Online |
| Medium Flat Rate Box, top-loading | 11 1/4″ x 8 3/4″ x 6″ | $13.75 Commercial Base $15.50 at Post Office & Online |
| Medium Flat Rate Box, side-loading | 14″ x 12″ x 3 1/2″ | $13.75 Commercial Base $15.50 at Post Office & Online |
| Large Flat Rate Box | 12 1/4″ x 12 1/4″ x 6″ | $19.30 Commercial Base $21.90 at Post Office & Online |
| APO, FPO, DPO Flat Rate Box | 12 1/4″ x 12 1/4″ x 6″ | $17.80 Commercial Base $20.40 at Post Office & Online |
| Large Flat Rate Box | 24 1/16″ x 11 7/8″ x 3 1/8″ | $19.30 Commercial Base $21.90 at Post Office & Online |
Maximum Weight and Size Requirements for Flat Rate Boxes
The maximum weight requirement for all the sizes mentioned above is 75 pounds. If the weight is higher, the flat rates won’t apply. As for the size, the maximum size on the thickest part of the box can be as much as 108 inches. The flat rate also doesn’t apply for items that are prohibited, restricted, and hazardous. Cigarettes and smokeless tobacco also fall under this. So if the box contains any of these, there will be special regulations and the flat rate won’t apply to it.