My STD wasn't any heavier than a regular letter so just a normal stamp worked. For my invitation I had to go with the 64 cent wedding postage stamp because it was a bit heavier. Definitely take them in to be weighed before shipping, I've heard stories of them being too heavy and getting sent back for insufficient postage!
I did save the date magnets but it got buy with still being regular first class mail (.44 at the time)
Invitations were pocket fold with 3 cards, invitation, and return envelope and was .64 cents - but yes, definitely weigh it at the post office first. They also had a wedding cake design for the .64 but not sure if they still offer that.
For our invitations, I originally planned on $0.64 based on the weight (ordered them from Zazzle), but then found out that they needed higher postage because they were square pocketfolds (if I remember correctly...) so I had to order more to reach the total of $1.08 each.
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