I have some clients are 'generous' with their borders. Sooo...I find a spot around the middle of the quilt to get a width, and use that as the width of the quilt. It keeps me from ending up with hourglass shapes and apple shapes. Silly me....I like them to end up SQUARE!!
For example: If I just used the measurement on the border, it might be 100", but the measurement through the middle might be 98". I want the top and bottom to be 98" also. I put a pin straight up on the back&batting at center, then one each direction 49" away, so I know where the edge should be. Hopefully, the 1" extra each direction is well distributed and not hard to work in.
Clear as mud?