Since I have purchased nearly all of my rulers when JoAnn's had a 50% off (or more) coupon, I have a lot of different sizes of rulers. The larger ones (8.5 or larger) I use mostly at home. However, since I go to the senior center to sew, I find that I take the rulers that will fit in my rolling sewing case, which are the 6.5 rulers. In either case, I usually use two rulers to measure, rather than using the lines on the cutting mat. One ruler that I use a lot is the 6.5 x 24 Lipfa ruler. I like this ruler because it will fit on the edge of the cutting mat or if you are cutting a stack of fabric, you can fit it up to the edge of the fabric and I always know that my cut will be perpindicular to the fabrics edge. I hope that I didn't make that last sentence clear as mud and it made sense to all.