Abstract: A base plate bolt hole marker is shown of the type used to mark bolt holes on a base plate in slab construction where foundation bolts are provided at spaced intervals along the edge of a concrete slab. The marker includes a handle portion and a measuring arm slidably received within the handle portion. The measuring arm has a bolt engaging end for engaging the foundation bolts. A marking member carried on the measuring arm is used to mark the location of a bolt hole on the base plate. A depending flange affixed to the handle portion of the device is used to align the device with the edge of the base plate whereby the measuring arm extends generally perpendicular to the axis of the base plate when the depending flange contacts the base plate. The distance between the bolt engaging end of the tool and the depending flange is adjustable by varying the position of the measuring arm with respect to the handle portion to mark bolt holes in base plates of varying widths.