An extendable measuring tool for measuring an alignment of a door or window frame. Specifically, the measuring tool is configured for determining if a door or window frame is out of square by measuring various regions of a frame and comparing the measurements to each other. In aspect of the invention, the tool includes a first carrier member having a channel and a first cap fixed to one end, and a second sliding member having a measuring scale on one surface and a second cap fixed to one end, wherein the second sliding member is at least partially disposed within the channel of the first carrier member and slides therein.