How to create an automatic cut list for lengths and widths

I have an estimate sheet that i use to prepare quotes for window trim. So i input the list one row will have all the information on the window and how much it will cost. So at the end of the row it displays, for example, 10ft, 10ft, 6ft, 6ft. So that would be displaying the width, width, height, height. Then maybe the next window would be 6, 6, 7, 7. The material that i purchase we get in 20ft parts. So you could go through that and do the math to determine how many 20ft portions i would need. Is there a way to create a formula that would automatically do that for me? without plugins