Hello,
A few days ago, I decided I no longer wanted to calculate floater border measurements on the back of whatever scrap of paper I had handy. Why not let a spreadsheet do the work for me?
Here is a link to the Excel file I created:
drive.google.com/file/d/0B9wbK1LPDOa7Nmg3MV9zR0ROVjQ/view?usp=sharing
Visit the link and click the download icon in the upper right-hand corner. The file will download. Look for it in your Downloads folder or desktop - depending on where you have your computer set to store downloads. The file name is floatercalculator.xlsx. You might want to put it somewhere safe so you can find it again.
To use the calculator, open your downloaded file with Microsoft Excel 2007 or newer - including Excel on an Apple computer! Enter your quilt's measurements in the light blue boxes. The spreadsheet will calculate the cutting width for your floater border(s) - both single and double. As you already know, two floaters should be cut the length of your quilt center and two the length of your short border.
Be wary of putting your cursor anywhere except in the light blue boxes so you don't accidentally change the formulas. If you do, just download a fresh copy of this file from the link.
Becky