I want to make a full bed size quilt for a friend for Christmas. I want to make it in patches 5" squares. How many squares will I need?
Is there any formula for working out the information for different bed sizes? Thank you!

Full size means different things to different people. How big do you want the quilt to be in inches?

to make a full quilt 81x96 with a 2" and a 6" border, you would need, with 5" finished sqares [cut 5.5"] 13 sq across and 16 sq down or 208 squares. if the sq start as 5" and finish to 4.5, you would need 15x18=270 sqs but reduce the outer border to 5"

Or does she want to use squares that are cut into 5x5 inch pieces?