Summarize the following:
Measure across the longest part of your quilt and across the shortest part. If your quilt is square, then the length and width measurements will be the same. Write down the measurements. You can measure in inches or centimeters. Either is fine as long as you stay consistent and use the same measurement throughout this process. This will give you the perimeter of your quilt. For example, if the width of your quilt is 40 inches (100 cm), then your width times 2 will be 80 inches (200 cm). If the length of the quilt is 50 inches (130 cm), then the length times 2 will be 100 inches (250 cm). Adding the length and width together will give you a total of 180 inches (460 cm) for the perimeter. After you find the perimeter, add 10 inches (25 cm) to the total. This will provide some extra length to overlap the binding. For example, if your perimeter is 180 inches (460 cm), then adding 10 inches (25 cm) would give you a total of 190 inches (480 cm).

Summary:
Measure the length and width of your quilt. Multiply each measurement by 2 and add the totals together. Add on 10 inches (25 cm) for the overlap.