Methods for estimating the root length in a sample using the line intersect principle were compared. One method involved visual techniques and used simple equipment. Another method introduced a new machine designed to estimate root length automatically. Either method had a high degree of accuracy, comparable with or better than other reported methods. Furthermore, the methods were tested over a wide range of root lengths up to 50 m. Even larger samples could be estimated using a reliable sub-sampling technique. The development of the root machine enabled the estimation of root length to become a simple laboratory routine.