The largest size envelope that can be mailed with a 45-cent stamp typically falls under the category of a "letter" by USPS standards, which is up to 11.5 inches long, 6.125 inches high, and 0.25 inches thick, weighing no more than 1 ounce. For larger dimensions or heavier weights, additional postage would be required. Always check the current USPS guidelines for any updates or changes in pricing.
The largest letter that can be mailed with a regular stamp is 11 1/2" X 6 1/8." Further info can be found on the official USPS page at: https://www.usps.com/send/can-you-mail-it.htm?#3
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.
US Mail standard envelope up to 1 ounce in weight needs a 42 cent stamp (or any combination of stamps that total 42 cents.)
You can typically mail one letter-size page in a business envelope with one first-class stamp. If you include additional pages, the envelope may exceed the weight limit for a single stamp (1 ounce). For every additional ounce, you'll need to add more postage. It's always best to check with your local postal service for the most accurate and current guidelines.
One 49-cent stamp should be all that is needed.
It depends on what country you are posting from, where to and, possibly, the weight of the package.
Postage is determined by weight and by size. An envelope with three pieces of normal paper can normally be sent with one first class postage stamp. Additional stamps may be required based on additional ounces and on the size of the envelope.
What is the standard-size large envelope?
If it fits in a standard business size envelope, regular domestic postage stamp.
Not all paper has the same thickness or size, but if you are using the most usual type of paper, you can mail four sheets with one regular stamp.
You can send up to five sheets of paper in a regular or business size envelope for one 42¢ stamp, to any state.
For a standard size envelope it is 44 cents.