Both of these envelopes have the same final size of 3 5/8" x 6 1/2", or 3.625" x 6.5". The difference is the size of their flaps and their utility #6 3/4 Regular: 3 5/8" x 6 1/2" - Commercial envelope with typically a 1.25" diagonal flap. #6 3/4 Remittance: 7 1/4" x 6 1/2" when flat, 3 5/8" x 6 1/2", or 3.625" x 6.5" when closed - A Donation envelope with expanded areas to print on the oversized flap which is 3.375" tall. Attached are the templates for a # 6 3/4 Regular and a # 6 3/4 Remittance Envelope
​https://www.4over4.com/blank-templates/envelopes