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It’s best to get your flag stand first so you can measure the material to fit. Cut a length of your main flag material to the width of the hanging bar of your flagpole. Most flag poles are around 12 inches (30.5 cm) wide on the horizontal pole from which the flag will hang. So cut your flag material to 12 inches (30.5 cm) width (or whatever the appropriate measurement it) or very slightly narrower.. Most flag poles are around 18 inches (45.7 cm) tall. Allow 4 inches (10.2 cm) length for the hanging flap, then cut your flag material an additional 18 inches (45.7 cm) long i.e. 22 inches (55.9 cm).  If you are growing tall plants underneath the flagpole, consider making the flag shorter in length so it will all be visible above the plants. The main thing is that the material should not touch the ground as it will get wet and muddy. You might like to double it the flag length to provide extra weight and make it hang better. Lay your flag material out on a flat surface. If you are doubling up the material, do that now and glue the two sides together along the left, right and bottom sides.  At the top of your flag, fold over a 4 inch (10.2 cm) piece of material. This will create the pocket that the flag rod will insert into in order to hang your flag.  Glue or stitch along the bottom horizontal side of this flap but do not glue the left and right sides as this is where the flap pole will insert into. Now that you have made the main part of your flag, you can do the creative design using the ideas in the section above.   Stitch, glue or paint your design onto the flag background you have created. A bright design can work very well, but remember some colors may fade over time.

Summary:
Measure your material against the flagpole. Decide what vertical length you want your flag to be. Stitch or glue the flag. Decorate your flag.