That will depend on the value of the stamps and perhaps the dimensions of the envelope. If you have the right values, it would only be one, but it could be a dozen or so if you only have smaller values. Check your Post Office web site for the specific rate necessary.
I think you mean 9x12 envelope.
A 4-ounce large envelope currently costs $1.57.
Two stamps
That depends on where you are sending it from (you country of origin) and to (the country of destination).
how many stamps for a 10.4 ounce envelope
To mail a 9x12 envelope weighing 3.8 ounces, you typically need two First-Class stamps, as the first ounce costs one stamp and each additional ounce costs an extra stamp. Since the envelope weighs 3.8 ounces, it falls into the 3-ounce rate category, which requires two stamps. Check with your local postal service for any changes in rates or requirements.
To mail an envelope weighing 1.5 ounces in the United States, you typically need two first-class stamps. The first stamp covers the base rate for up to 1 ounce, and the second stamp accounts for the additional weight. Always check the current postal rates, as they can change.
The first ounce will cost 44 cents. Each additional ounce, or fraction, is another 17 ounces. That would be 78 cents for that envelope at the start of 2011.
The number of stamps needed to send a 9x12 envelope depends on its weight and the mailing service you choose. For a standard 9x12 envelope weighing up to 1 ounce, you typically need two First-Class stamps. However, if the envelope exceeds 1 ounce, you'll need additional postage based on the weight. It's best to check the current USPS rates or use their online postage calculator for accurate pricing.
Take your envelope to the Post Office and they will weight it, and give you your answer as the cost of mailing anything is done by weight.
As of June 10, one ounce of first class mail is 44¢. Every additional ounce is 20¢. So, a six ounce envelope would cost $1.44 to mail, or four forever stamps.
The amount of stamps needed for an envelope is determined by weight. Weigh your a4 envelope and you will know how much postage is needed.