I think you mean 9x12 envelope.
how much postage for a 9x12 envelope weighing 6.6 ounces
how much postage required for a 9x12 envelope weighing 4.6 ounces
$3.04 as of 2016.
$3.04 as of 2016.
Those dimensions make it a large envelope, so postage starts at 94 cents (two Forever stamps) for the first ounce, and more if it's heavier.
Postage depends on which country you live in, how much the envelope and contents weigh, and where you are sending the envelope to. You'll need to include all that in your question to get the correct answer - or you could just go to your local postal website and get the answer from the experts...
.92
Calculate it on usps.com
To mail a 9x12 envelope weighing 14 ounces within the United States, you would typically need to use Priority Mail, as it exceeds the weight limit for First-Class Mail. As of my last update, the cost for Priority Mail starts at around $8.70 for packages weighing up to 1 pound, but prices can vary based on distance and specific service options. It's best to check the USPS website or visit a local post office for the most accurate and current rates.
At least two for those dimensions, possibly more depending on weight.
9x12 = 108