At least two for those dimensions, possibly more depending on weight.
4
Depends where it's going to
100
How many stamps to STOCKHOLM
If you are sending a three paged letter it is around three US stamps!!!!
3 stamps!
That is what stamps are for, to pay postage. In the US you buy postage stamps and put them on mail to any other country in the world.
You need one if its a letter and like a whole bunch if your mailing a box.
4 stamps
1
No you cannot use US stamps. Items mailed must have the stamps of the country of origin on them. Most shops will be able to provide you with the appropriate stamps to use to mail with their cards, or visit their post office!
3 stamps.