Abstract: An extensible carpenter's level includes a pair of body members in end-to-end relationship and a pair of extenders mounted in face-to-face relationship on the body members. The extenders are slideably retained in tracks on the body members. The body members have longitudinal slots and the extenders have locking means passing from the extenders through the longitudinal slots on the body members for locking the body members and extenders into relative position. The body members, and preferably also the extenders, have level indicating means thereon, and are separable from the device as a whole for convenient individual use. When assembled, the body members can be slided apart to accommodate a desired length within a span up to about twelve feet, the reference edges of the body members remaining co-linear at any extension length.