A die line is the exact size and shape you want your custom label to be once it is finished or trimmed. You can have any shape or size for a custom die line. However, you will need to ensure it is in your file on a separate layer. In its simplest form, a die line is a shape in Illustrator with a stroke of at least 0.5 pt in a spot color that is not used anywhere else in the file. Die lines are extremely important in your file regardless of shape or size. We need to make sure your final label size is correct, including a die line helps us both. Before you create your die line, you need to make sure your document is set up correctly from the start. This is an essential but often overlooked step.
Now that you have the file size (artboard) and bleed set up. You can create the die line. There are a few steps you need to do before creating the shape. Using the same 4” x 4” trim size (also the same size as your artboard as assigned above.