I can't go to her house to be sure it's measured properly. She is in Nova Scotia & I am in Florida. Just not feasible!! I will try again to ask her for measurements, but she's having family issues at the moment. If 39" x 80" is the mattress top, 12-1/2" of border all around should be sufficient, but I will try to get her to measure for me. I want to start cutting all the 2-1/2" squares I'm going to need! Thank you all for your help!!