If you're replacing an existing door or adding a new entryway to your new or existing home, you'll need to know how to install a prehung door. The process does have several steps, but is easy enough to be done by just about anyone who want to engage in some DIY beyond painting or hanging artwork. Before any entryway design choices can be made, you must know whether the door will be hung with opening/closing hardware on the right or left of the door (from the interior perspective). Once you know which side your knob and lock will go, and which side your hinges will be on, you'll know when you order your prehung door to choose left-hand swing or right-hand swing — this allows the door-maker to add the appropriate holes in the right places on the slab that will become your door.

Before Prehung Door(s) Arrive, Before Removing Packing Case: Drywall and Flooring

Before you get into the more intimate details of how to install a prehung door, and before it even comes out of the box it came in, there are two critical details you’ll need to ensure have been completed. The first step is to ensure the floor where the door will be installed is level. All you need to ensure a level flooring where you’ll install your door is a simple hands-free level — place it on the flooring where the prehung door will go. If the bubble is not in the middle, you’ll need to sand down whichever side is making the bubble inside hands-free level tilt to one side or the other.

How to Install a Prehung Door: Measuring the Frame Before Unpacking

Once your new prehung door has arrived, but BEFORE you remove it from the packing case, measure from one end outside of the frame to the other to get the exact, correct width of the entire door, including the doorframe. Once you know this measurement, you can measure the open area where the door will be installed — if there’s too much drywall, you’ll need to sand down to allow enough space for the entirety of the door, including the doorjambs and frame, where hardware affix to. If there’s not enough space, you’ll have to sand down or cut away drywall, wood, or brick (whatever the material that will surround the doorframe is) until there’s enough space for the doorframe and door to fit in.

Unpacking: How to Install a Prehung Door — Doorframe First, then Door Installation

After you’ve unpacked the doorframe and door and installed the doorframe in the open area, no matter how well you measured, there will be some open areas on the right and left side as well as the top and bottom of the frame. To close these areas up, you will use a combination of shims (small pieces of wood) and spackle: first attach shims using a nail gun, then spackle once doorframe is firmly in place.
The next step in how to install a prehung door is to install the door itself into the frame, and finally, install your hardware, including knob, lock, hinges, and any accessories or embellishments you may have picked out. In these final steps, be sure you ensure the door is level from side to side and is measuring accurately within the frame from top to bottom before committing to any new nails or screws, as you move through the phases of securing the door to the frame. Once you’ve installed the door and ensured it swings as it should within the doorframe, add your hardware and the job is complete. Now that you’ve done it yourself once or twice, you can show others how to install a prehung door!