Not just Idea

Say, whats a tape measure done for you lately? After many years of woodworking, I discovered that I was using tape measures less and less. When I can, I dont use one at all, opting for memory sticks or cutting notches in a board at whatever length is needed. In other words, using unitless measurements based on the actual lengths needed. Its actually far more accurate than a tape measure.  

But there I times when I just need to calculate a few rough estimates. There are countless ways of measing stuff without a ruler. Let us know if you have some more ideas! Here are a few that I use: