How to install a prehung interior door (and where DIYers go wrong)

Hanging a prehung interior door is one of the most satisfying jobs a homeowner can take on — and one of the easiest to get subtly wrong. The unit shows up looking finished: slab mounted, hinges set, jamb square in the crate. It feels like you just slide it in and nail it. But a door that swings open on its own, drags the strike, or shows a fat reveal on one side and a hairline on the other is the tell that the jamb went in racked. This is a real, doable weekend job. Here's the method a finish carpenter actually uses, the why behind each step, and the exact places DIYers lose the fit.

Tools and materials you'll need

None of this is exotic. If you own a decent cordless drill and a level, you're most of the way there. The two things worth not skimping on are a good level and real tapered shims — a bundle of cedar shims is a couple of dollars and does the whole job.

• A 4-ft level (a 6-ft is better on a standard door) — plus a short torpedo level for tight spots.
• Cedar tapered shims — a full bundle. You'll use more than you think.
• Finish nailer or 8d/16-ga finish nails and a hammer — plus a nail set if you're driving by hand.
• 2-1/2" or 3" screws to swap into the top hinge (the trick below).
• Utility knife, flat bar, and a small block plane or chisel for shim trimming.
• Tape measure, pencil, and a couple of scrap 1x blocks to gauge floor clearance.
• Casing, brad nailer, and caulk for the trim-out.

Step one: check the rough opening before the door goes anywhere near it

Every clean install starts here, and it's the step people skip. A standard prehung wants a rough opening about 2 inches wider and 2 inches taller than the door unit — that gap is your shim room. Too tight and you can't square the jamb; too loose and you're spanning air with shims. Measure the width at top, middle, and bottom, and check the opening for plumb on both sides with your level. Most framing is a little off; that's normal. What you're doing is finding out how far out it is so nothing surprises you once the door's set.

Two things matter more than perfect framing. First, check that the subfloor across the opening is level — if one side sits high, the door will lean and every reveal after that fights you. Second, look at the wall itself: if the finished wall is out of plumb front-to-back, you'll want to set the jamb to split the difference so the casing sits flat on both faces. Confirm the floor and both trimmer studs before you commit a single nail.

Step two: set the hinge jamb plumb — this is the whole job

Stand the unit into the opening from the side you want the door to swing toward, and get the jamb roughly centered in the gap. Everything now hangs on the hinge side. The hinge jamb is the reference edge — get it dead plumb and shimmed solid, and the door hangs true on its own weight. Get it wrong and no amount of fiddling on the latch side saves you.

Put your level on the face of the hinge jamb and shim behind each hinge until it reads plumb in both directions — side to side and, just as important, front to back so the jamb isn't leaning into or out of the room. Slide shim pairs (one from each side, tips opposite) in behind the top hinge first, tack it, then the bottom hinge, then the middle. Snug the shims so they support the jamb without bowing it — over-driving a shim pushes the jamb out of plumb and racks the frame, which is exactly the failure you're trying to avoid. Check plumb again after every hinge.

Step three: the long screw trick, then set the reveal even

Before you touch the latch side, back out the top screw in the top hinge and replace it with a 2-1/2" or 3" screw that reaches past the jamb and bites the framing (the trimmer stud). Factory hinge screws only grab the jamb; a long screw ties the whole door back to the structure so it can't sag over the years. This one screw is the difference between a door that still swings true in five years and one that starts dragging.

Now work the latch jamb and head to set the reveal — the gap between the door slab and the jamb all the way around. It should be even top to bottom and side to side, roughly a nickel's thickness. Close the door most of the way and read the gap. Shim the latch jamb top, middle, and bottom to make that gap consistent, adjusting until the slab tracks parallel to the jamb the whole swing. A reveal that's tight at the top and open at the bottom (or the reverse) means the frame is racked — go back to the hinge side and re-check plumb rather than trying to shim your way out of it on the latch side.

Step four: nail it off, then check the latch

Once plumb, level, and reveal all read right with the door closed, fasten through the jamb at every shim location so you're nailing into solid backing, not spanning the gap. Two nails per shim pair, one near each edge of the jamb so the stop and the casing side both stay put. Score and snap the shim tips flush with a utility knife so they don't hold the casing off the wall. Then swing the door slowly a few times — it should stay put wherever you leave it. A door that creeps open or shut on its own is telling you the jamb still isn't plumb; fix it now, before the casing hides the shims.

Last, check the latch. Close the door and watch the latch bolt meet the strike plate. It should slide in and catch on the first push without lifting or forcing the door. If it's high or low, the reveal is off and the fix is back at the shims, not at the strike. Only once the reveal is even should you fine-tune the strike plate itself.

Where DIYers get stuck

Almost every bad prehung install traces back to one of a short list of mistakes. Knowing them ahead of time is half the battle:

• The racked jamb. The number-one failure. The hinge side went in a hair out of plumb, so the reveal wedges — tight on one end, gapped on the other — and the door drifts. It's not a latch problem; it's a plumb problem two steps upstream.
• Over-driven shims. Cranking a shim to "make it tight" bows the jamb inward, which throws off the reveal and can bind the slab. Shims support; they don't clamp.
• Skipping the long screw. The door hangs fine on day one, then sags months later as the weight works on short factory screws. Two minutes now saves a callback to yourself.
• Ignoring the floor. Setting a plumb jamb on an out-of-level floor means the door leans, and you'll never get the reveal even. Check the floor first.
• Nailing before it's dialed in. Once the nails are in and the casing's on, every mistake is now permanent. Verify the swing and the latch before you commit.

Case it out — and when to call a carpenter

With the door hung true, the casing is the reward. Miter the outside corners at 45 degrees, hold a consistent reveal off the jamb edge (an eighth of an inch is standard), and pin the casing to the jamb and into the framing so it pulls tight to the wall. Caulk the wall side, fill the nail holes, and you've got a door that looks like it grew there. If you're weighing panel doors against flat slabs for how the casing reads, our guide to interior door styles walks through the options.

Here's the honest part. One prehung door in a forgiving opening is a great DIY project, and if yours came out with even reveals and a latch that catches, you've done the work. Where it gets hard fast is volume and out-of-square: a whole house of doors, an old opening that's racked and settled, or a jamb that has to be scribed to a wall that's nowhere near plumb. That's finish-carpenter territory, where the fit has to be right on every one and the schedule doesn't allow re-hangs. If you're deciding between ordering prehung units or slabs for a build, we break that call down in prehung vs. slab doors, and the levers that drive door-hanging cost — count, opening condition, paint- vs stain-grade, and casing profile — are laid out in our finish carpentry cost guide. There's no flat rate that survives contact with a real house, so door work is quoted to the openings.

Hanging one door yourself? Go for it — this guide is the whole method. But if you've got a stack of them, an old house full of out-of-square openings, or a build that can't afford a single dragging door, that's what we do all day. See how we handle interior doors, or send us the count and we'll bid the openings.