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.
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.
.44
.44
.44
75
45 cents
For flat paper items, postage goes by weight, not by size.
1.22
6.3oz
The postage is standard first class 1 ounce (a "Forever" stamp).