We frequently get asked about postage rates for invitations. Although rates are changing all the time, the USPS recently sent out this super helpful guide to mailing first class mail. Always double check with your postmaster before mailing invitations though - you just never know.
We should also note that the cotton paper we print on is ever so slightly thicker than 0.016".
If you're mailing one of our letterpress reply postcards be safe and use a 49 cent stamp!