Both of these envelopes have the same final size of 3 7/8" x 8 7/8", or 3.875" x 8.875". The difference is the size of their flaps and their utility #9 Regular: 3 7/8" x 8 7/8" - Commercial envelope with typically a 1.25" diagonal flap. These are the perfect size for a return envelope that fit nicely inside of a #10 envelope. They are available with or without a window. #9 Remittance: 7 3/4" x 8 7/8" when flat, 3 7/8" x 8 7/8", or 3.875" x 8.875" when closed - A Donation envelope with expanded areas to print on the oversized flap which is 3.625" tall. Attached are the templates for a # 9 Regular and a # 9 Remittance Envelope 9_
​https://www.4over4.com/blank-templates/envelopes