A multi-function layout square of modular construction having a laser that is capable of performing multiple functions is disclosed. The multi-function square has a metallic outer casing with magnetic properties, with a protractor plate slidably, pivotally, and removably attached by thumbscrews to the casing that can be moved and rotated with respect to the casing and slid linearly along a portion of the length of the casing. When the protractor plate is removed the casing may be used as a level, a plumb bob, a ruler, and a compass. When the protractor plate is attached the tool may be used as a framing square, roofing framing square or rafter square, and a gauge or scribe for straight lines, arcs, or circles. The laser, a switch, and a pair of bubble level vials are contained in a module installed at one end of the casing, and a second module containing batteries is removably installed at the other end of the casing. Each module has electrical contacts that engage the interior surface of the casing and contacts that engage the batteries when the modules are installed and abutted. When the switch is on, a circuit is completed through the metallic casing, which electrically connects the batteries to the laser. The casing may be suspended vertically from a support surface by passing a string or wire through a bore in one of the thumbscrews, may be mounted on a tripod, or may be magnetically attached to metal objects.