It is not only us that have to worry about the weight, length, width and thickness of parcels we send. Now the US is introducing the same system. CNN reports:

The postal rate increase that kicks in Monday is shaping up to be a big headache for many businesses.
Many companies say they are confused and frustrated as they try to adjust to the new rules, and some say mailings could be severely curtailed due to higher postage costs.
The new regulations mean larger envelopes and packages will automatically cost more than smaller mail. Currently, postage is determined by weight, unless it's an especially large or odd-shaped package that warrants special handling.
If your solution come Monday is to stuff the same amount of material into a smaller envelope, the Postal Service could get you there, too: There are new thickness restrictions.