How to Install Interior Door: Step-by-Step Guide

A door that swings shut on its own or refuses to latch is almost never a bad door. It is a bad installation. Learning how to install interior door units correctly comes down to one skill: getting the frame perfectly plumb and level before a single nail goes in. Master that and the door hangs true, the reveals stay even, and the latch clicks home every time. This guide walks through a prehung interior door install from rough opening to finished trim.

Part of our Windows & Doors guide — explore the full guide →

Prehung vs Slab Doors

A prehung door arrives already mounted on hinges inside its own frame, ready to set into the rough opening. A slab is just the door panel, meant to be hung in an existing frame with new hinge mortises and a bored latch. For most homeowners, a prehung unit is far easier because the hard geometry is done at the factory.

This guide focuses on prehung installation, which is the right call whenever you are building new or replacing both the door and its frame.

Tools and Materials You Will Need

Gather everything before you start so you are not hunting for a shim mid-install.

• 4-foot level and a shorter torpedo level
• Cordless drill and finish nailer or hammer and finish nails
• Wood shims (a full bundle)
• Utility knife, tape measure, and pencil
• 2.5-inch and 3-inch screws for the hinge jamb
• Pry bar and safety glasses

Step 1: Check the Rough Opening

A standard rough opening is about 2 inches wider and 2 inches taller than the door’s nominal size to leave room for shimming. Measure the width at top, middle, and bottom, then check that the floor across the opening is level. If one side sits high, you will need to trim the opposite jamb leg later so the head stays level.

Confirm the floor finish height too. If flooring is going in after the door, plan the jamb-to-floor gap accordingly.

Step 2: Set the Door in the Opening

From the side the door swings toward, tip the prehung unit into the opening and center it. Rest it on the finished floor or on spacers if flooring comes later. Have a helper hold it steady, or use a couple of shims to wedge it upright while you work.

The hinge jamb is your reference. Everything you do next revolves around making that side perfectly plumb.

Step 3: Plumb and Fasten the Hinge Side

Place your 4-foot level against the hinge jamb and adjust until it reads plumb in both directions. Slide shims behind the jamb at each hinge location, tapping them in pairs from opposite sides so they stay flush without bowing the jamb.

Once plumb, drive a nail or screw through the jamb and shims near the top hinge. Recheck plumb, then fasten at the middle and bottom hinges. For extra strength, replace one screw in each hinge with a 3-inch screw that reaches the framing stud, which keeps a heavy door from sagging over time.

Step 4: Set the Reveal and Latch Side

With the hinge side locked in, close the door partway and look at the reveal, the gap between the door edge and the frame. It should be an even 1/8 inch all the way around. Shim the latch-side jamb behind the strike plate and at two or three more points, adjusting until the reveal is uniform top to bottom.

Fasten the latch jamb through the shims once the gap is even and the door closes without rubbing or springing open. Test the latch. It should engage the strike smoothly without lifting or pushing the door.

Step 5: Trim the Shims and Add Casing

Score the protruding shims with a utility knife and snap them off flush with the wall so the casing sits flat. Run a bead of low-expansion foam sparingly around the jamb only if the gap is drafty, since too much foam can bow the frame.

Install the casing with a consistent reveal along the jamb edge, usually 3/16 inch. Nail the casing to both the jamb and the wall framing, then set and fill the nail holes before caulking and painting.

Common Mistakes to Avoid

Rushing the plumb step is the number one error, because every later problem traces back to a frame that is out of true. Other pitfalls include over-shimming until the jamb bows, forgetting the long hinge screw that prevents sag, and nailing the casing before confirming the door still swings freely.

Handling an Out-of-Level Floor

Few floors are perfectly level, and this trips up more installs than any other surprise. If the floor slopes across the opening, the door frame will lean and the reveals will run off. The fix is to shim the low side up or trim the high-side jamb leg so the head jamb sits perfectly level even though the floor is not.

Check the floor with your level before you set the unit. If one side is high by half an inch, cut that jamb leg down by the same amount. Getting the head level is what keeps the door from swinging open or closed on its own once it is hung.

Adjusting a Door That Won’t Latch

Even a careful install sometimes needs fine-tuning. If the latch misses the strike plate, the frame likely shifted slightly during fastening. Look at where the latch bolt hits relative to the strike hole and adjust the strike plate up, down, or sideways, filing the opening slightly if needed.

If the door rubs the jamb on one edge, a shim behind the hinges usually corrects it. Adding a shim behind the top hinge swings the door edge one way, while shimming the bottom hinge moves it the other. Small adjustments here make the difference between a door that sticks and one that closes with a satisfying click.

Finishing Up

Knowing how to install interior door units is really about patience with the level and the shims. Take your time on the hinge side, keep the reveal even, and back up at least one hinge with a screw into the stud. Do that and you will hang a door that closes cleanly, latches every time, and looks like a professional set it.