Which tool is best suited for squaring a 36-inch pre-hung door?

The best tool for squaring a 36-inch pre-hung door is the framing square. A framing square, also known as a carpenter's square, is specifically designed for making precise measurements and ensuring right angles. When installing a pre-hung door, it is essential to verify that the door frame is square to ensure proper operation.

The framing square has a large, flat body and an arm that helps check the squareness of corners by outlining and measuring the distance diagonally across the frame. By taking measurements from one corner of the door frame to the opposite corner, the installer can determine if adjustments are needed to achieve a perfect square. This is critical, as doors that are not square may not close properly or may bind against the frame.

While other tools can assist in the installation process, they do not serve the primary function of checking squareness in the same effective manner as a framing square. For example, a combination square can also measure angles and check for squareness; however, its smaller size makes it less suitable for larger frames. A 4-foot level is excellent for checking horizontal and vertical plumb but does not directly verify squareness. A plumb bob is useful for ensuring vertical alignment but is not effective for addressing the squ