To select the right size quilt, you need to consider four factors. The most obvious is the size of your bed, a King size bed requires a bigger quilt than the quilt that would be used on a Full size bed.
The second factor is the length of the drop. The drop length (overhang) is a matter of taste and practicality. The most common drop choices are:
Usually, quilts for King and Queen size beds fall between Coverlet and Blanket size. A bed skirt is used to cover the box spring when a quilt close to Coverlet size is used.
The third factor is the style of your bed. Most beds today do not have Footboards, so there must be a drop on the sides and the foot for these beds. If your bed has a footboard, you only need a drop on the sides.
The final factor is the treatment of your pillows. Most people like to cover their pillows with the quilt. To do this, an allowance for a "pillow tuck" of 10" to 18" is required depending on the thickness of the pillows. Many people, alternatively, use pillow shams (decorative pillow covers) eliminating the need for the "pillow tuck" allowance.
In considering the right quilt size, bear in mind that hand quilted quilts are quilted on a quilt frame. In Lancaster, Amish women use frames which are typically 110" to 116" wide. While it is possible for a quilt to be made upto 120" long, a quilt can not be wider than the quilt frame used in making it.
The interactive table below may help you determine the right size for your quilt.
Some quilts can be used either lengthwise or width-wise. Some can't. Many quilts have a special design on the head where the pillows are expected to be, or the quilt design includes elements (for instance a large heart) that demand that the quilt be used in a single orientation. Other quilts are symmetrical and can be used in either orientation.
Be careful when looking at the dimensions of non-symmetrical quilts. The length of a non-symmetrical quilt made for a King size bed will be smaller than its width. For Queen and Full size beds, the length will be larger than the width.
Many applique quilts are designed to be specifically used on queen size beds and even though some of these may be big enough to be used on king size beds, they won't look good when so used.