You take the length you need and divide it by 36. I'd add 10 inches to your length to allow enough extra for quilting. So that's 125 divided by 36. That's 3.4. So I'd round up to 3.5 yards length. You'll need three widths of fabric to cover 115 inches but it won't be quite 10 inches extra.
The two base number are always 36 inches in a yard and 40 inches of useable fabric width.