This is a guide to the classic #10 window envelope, the old standby of direct marketing. A #10 is 9.5" wide and 4-1/8" high. The internal proportions are detailed in the image below. For a PDF of the layout in its true size, click here.
This envelope was designed for use with a standard 8.5x11" sheet of paper. Given the fact that the paper will undoubtedly slide around in the envelope, 
the image below of the top third of a trifolded letter (three panels of 3-21/32" height) outlines the maximum "safe area" that a designer may set aside for an address with complete certainty that it will be visible through the envelope window. Want a life-size template? Click here for a PDF.
The old #10 is far from the only window envelope alternative. Below is a complete list of standard proportions, appropriated from the experts at www.windowenvelopes.com
| Standard Window Envelope Size: |
Envelope Measurements: |
Window Size: |
Window From Left: |
Window From Bottom: |
| #6 3/4 |
3-5/8" x 6-1/2" |
1-1/8” X 4-1/2” |
7/8” |
1 / 2” |
| #7 |
3-3/4" x 6-3/4" |
1-1/8” X 4-1/2” |
7/8” |
1 / 2” |
| #7 3/4 |
3-7/8" x 7-1/2" |
1-1/8” X 4-1/2” |
7/8” |
1 / 2” |
| #8 5/8 |
3-5/8" x 8-5/8" |
1” X 4” |
1” |
3 / 4” |
| #9 |
3-7/8" x 8-7/8" |
1-1/8” X 4-1/2” |
7/8” |
1 / 2” |
| #10 |
4-1/8" x 9-1/2" |
1-1/8” X 4-1/2” |
7/8” |
1 / 2” |
| #11 |
4-1/2" x 10-3/8" |
1-1/8” X 4-1/2” |
7/8” |
1 / 2” |
| #12 |
4-3/4" x 11" |
1-1/8” X 4-1/2” |
7/8” |
1 / 2” |
| #14 |
5" x 11-1/2" |
1-1/8” X 4-1/2” |
7/8” |
1 / 2” |
Need someone to write letter copy? Try Jeff Watter. He's a great copywriter who writes to fit...proportionately, and creatively as well.