The post office ships by weight only. If you are shipping anything under 13oz then you should ship it First Class Mail only...even if it is a small package. Anything over 13oz must be sent either priority mail, parcel post, or express mail. You can calculate all your shipping needs at USPS.com and even print labels at home.
Yes, postage is determined by weight category, not envelope size. Everything that weighs one ounce or less falls into the same weight category.
The current rate is 44 cents for the first ounce. The second ounce is 17 cents. There are also surcharges if the envelope is not a standard size.
A one ounce letter in an envelope of standard size and shape will be delivered for 44 cents.
For the first ounce it will be 88 cents. There is an additional charge for the larger size. Each additional ounce is 17 cents.
If in any doubt, take the letter to a post office. In the UK, apart from the weight, the size and thickness of the envelope can influence the final cost of postage.
There is not a set price based on the size of the envelope. The final amount of postage will depend on the weight, the destination of the envelope and the thickness and/or the rigidness of the parcel.
$0.98 for a standard letter size envelope weighing up to 1 ounce, United States to Germany. It's the same rate to all USPS "Group 5" Western European countries. Source: www.usps.com
For flat paper items, postage goes by weight, not by size.
It is not the size of the envelope that matters, it is the weight - it is probably best to have the package weighed at the Post Office to obtain the correct postage.
In the UK, it is not only the weight, but also the size and thickness of the envelope or package, and the destination (UK or abroad). It is best take take the envelope to a post office to ensure the correct postage is used.
Postage is by weight - not size where letters are concerned.
44 cents for the first ounce, 17 cents for each additional ounce. 5 times 17 is 85 cents plus 44 cents it would be $1.29. There may be additional fees for envelope size.