It depends on where you are posting from, where to, what the weight of the envelop is, whether or not you want First Class or express post or any other services.
Two stamps
Over 9000.
45 cents
For flat paper items, postage goes by weight, not by size.
One
The postage for a 6 x 9 envelope would depend on the weight of it.
The postage for a 6 x 9 envelope would depend on the weight of it.
1.22
6.3oz
A 6 x 9 envelope for a 1099 will cost you approximately $1.40. The exact amount will depend upon the weight of the package.
Two stamps
1.35
3
The cost for postage on the 9x11-inch envelope will vary depending on the weight. As of May 2014, the standard cost of a stamp is 49 cents in the United States.
Since the envelope is 5.25 X 5.25 inches square, the postage is .70 cents for first class. This rate is for an envelope that weighs .5 ounces. The postage may be higher depending on the weight of the envelope.
Over 9000.
.44