I've done this many times and it will work in a pinch. A dollar bill measures barely much over 6 inches of length. When a measuring tape or ruler is not within reach, a 6 inch dollar bill can give you a close figure. Fold in half, and it would be 3 inches. It is kind of handy to measure lengths of nails, bolts, screws, etc. It's not as precise as a tape measure, but will work.