If the stripes are horzontal, the widths available are limited. You're sewing all the strips together, cutting them in half, sewing those two together, so the width decreases by half the length each time unless you make some adjustments, such as sewing a third (or extra) row at some point (which will require planning by reducing the number of strips you start with), which will also change the length.
Here's a discussion of how to change the size.
http://www.quiltingboard.com/main-f1...t192039-3.html
If you're using your own strips, you may not be using whole jelly rolls (40 strips).
The name 1600 quilt comes from guessing that you have 40 strips with 40" useable WOF. Someone else suggested 41" useable WOF. If you're using diagonal seams, I think you would lose about 3" per strip. If you add a square in a contrasting fabric with each strip, you will gain 2" for each WOF.
If you're using a different number of strips than multiples of 40, you'll have to calculate what the width will be by dividing by 2 until you get to a width that you want. Then you can make other adjustments such as cutting lengthwise and adding a strip of fabric adding to the width. And there are borders you can add, ...