Final answer:
The correct side margin for a letter address on a large envelope is 1.5 inches, which ensures clarity for postal services and adheres to USPS guidelines.
Step-by-step explanation:
The side margin measurement for a letter address on a large envelope should be at least 1.5 inches from the left edge. When addressing an envelope, it's important to leave sufficient space for the recipient's address to be clear and for postal services to add any necessary barcodes or markings. The United States Postal Service (USPS) provides guidelines that recommend a clear area on the front of the envelope where the address should be located.
For a large envelope, also known as a flat, the recipient's address should be parallel to the longest side of the envelope. It is also crucial to ensure that there's enough space at the top and bottom of the address area to avoid any overlaps with postal markings or stamps.