There are four key steps in determining the measurement of an envelope:
1. Always have seal flap pointing up 2. Measure smallest dimension first 3. Measure larger dimension second 4. The location of seal flap determines style

The Style can only be Open Side or Open End

There are five steps to determining the positioning and measurement of an envelope window:
1. Position seal flap at top. Ignore the printing on the envelope. (Many envelopes are loaded by inserting equipment from the bottom, so this is an important point.) 2. Measure the window height 3. Measure the window width 4. Measure the distance from left edge 5. Measure the distance from bottom edge
These four measurements listed out give you the windows positioning.

The diagram below indicates the meaning of key standard envelope terms.

The diagram below indicates the meaning of terms associated with the executive envelope.

There are two main types of open side envelopes:

There are two main styles of open end envelopes: