On most musical instruments, especially on the guitar, it is possible to play the same note or chord in multiple ways. In this project, we develop a simple audio-based method to estimate the fingering of a note played on an acoustic guitar from a recording. Such a system has several applications, including musical training, musical education, or analysis of historical recordings. The advantage of our method with respect to the state-of-the-art is that it is simple and efficient: it uses a single feature, the inharmonicity coefficient. In spite of its simplicity, this method performs well in both synthetic and real audio recordings: the misclassification rate that we achieve is of 12.3 %.