You need to establish it's overall size and thickness, then it's weight also before you can ask the postage. The post office will be able to do this for you.
The postage is $1.76 for a standard letter envelope of 2 oz.
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.
Its 70 cents for sending a letter to any country in the EU. So, I guess that goes for England too.
63%
The postage rate to mail a 6x8 envelope in the United States as of 2014 is $0.44 if it is within the regulated weight. Additional costs may occur if it weighs more.
an 8x8 envelope is charged "parcel rate"..because it is square and over the letter size dimension...cant be a "large envelope" because it is not rectangular
Certainly, they are still valid for postage. You just have to use enough of them to equal the current postage rate for the envelope or package you are mailing.
Certainly, that is what they were created for, to serve as postage. Just make sure the total face value of the stamps equals the appropriate rate for the envelope or package.
This answer depends on several factors: the size and shape of the envelope, the weight of your letter, and how quickly you need the letter to arrive. It is a safe to estimate a little over $1.00 USD to mail a letter from somewhere in the US to London, but the exact cost will vary slightly.
As of May 2009, 1 ounce costs 44 cents, US
The US postage rate for inside the United States varies depending on service, such as first class mail, media mail, or bulk mail. It may also depend on services such as overnight or priority. The current postage rate for a stamp for a standard letter sized envelope is 46 cents.
An envelope with a height exceeding 6 and one-eighths inches, and any square envelope, is non-machinable. Therefore, the rate for first class US domestic postage is $.64.