Invitation Envelopes are referred to as the "A" sizes of envelopes.. "A" Envelopes are usually made from thicker paper stock as compared to commercial envelopes ( think #9 , #10), and usually come in a wider variety of colors and finishes than some of the other envelope sizes. A-Envelope Sizes (inches):. A1 - 3 5/8" x 5 1/8", or 3.625" x 5.125". A2 - 4 3/8" x 5 3/4", or 4.375" x 5.75". A6 - 4 3/4" x 6 1/2", or 4.75" x 6.5". A7 - 5 1/4" x 7 1/4", or 5.25" x 7.25". A8 - 5 1/2" x 8 1/8", or 5.5" x 8.125". A9 - 5 3/4" x 8 3/4", or 5.75" x 8.75". A10 - 6" x 9 1/2", or 6" x 9.5". You can purchase Invitation Envelopes at 4OVER4.COM in standard white. We also sell invitation envelopes in hundreds of standard and exotic colors, such as kraft, black, blue, red, pink, violet, lilac, moss, nude, canary, orange, green, you name it. At 4OVER4.COM, we take pride in having your project come to life. Don't see what you are looking for in our printed envelopes section? No Problem! Simply contact or Support Team at Support@4over4.com