How to Install Crown Molding

Crown molding transforms a room the moment you look up. That trim where wall meets ceiling stops looking like an unfinished edge and starts looking like a finished space. The work itself is exacting—corners are rarely true, ceilings aren't always level, and the math of miters keeps you honest—but it's learnable. You're not rerouting plumbing or rewiring outlets. You're fitting and fastening wood at one of the most visible spots in the room. Done well, it looks like it was always there. Done sloppily, every guest notices.

1. Know Your Room's Geometry. Walk the perimeter of the room and measure each wall. Note any corners that aren't 90 degrees by holding a speed square against the corner; most bedrooms have at least one corner that's 92 or 88 degrees. Identify which wall you'll start on—typically the wall opposite the door, where seams are less visible. Calculate the linear footage you need and add 10 percent for waste and testing cuts.
2. Dial In Your Angles First. Install a fine-tooth blade on your miter saw. Crosscut a piece of scrap molding at 45 degrees. Hold the two pieces together at the inside corner angle your room has—if it's square, they should meet flush. If they don't, your corner angle isn't 90 degrees and you'll need to adjust your miter angles slightly. Mark your saw fence or make a note on your saw's angle scale so you remember the correction.
3. Launch Strong on Wall One. Start on your planned wall with two 45-degree miter cuts (one on each end, forming an inside miter pair). Hold the molding tight to the wall and ceiling corner, then drive 2-inch finish nails through the back into studs and ceiling joists spaced about 16 inches apart. Use a stud finder if your wall edges aren't visible; a missed stud means the molding will flex. Sink nails below the surface with a nail set.
4. Seal Inside Corners Tight. Where your first wall meets the next wall, miter the end of your first piece and the start of your second piece so they form a closed corner. Caulk the gap lightly—crown molding caulk, not paintable caulk—then nail the second section. Inside corners are the joints your eye lands on first, so take extra time to close any gaps with caulk before it dries.
5. Perfect Outside Corners Early. Outside corners in a bedroom are less common but they happen when two walls turn outward. Cut complementary 45-degree miters on both pieces—one left, one right—and dry-fit them before fastening. The miter line should be crisp. Nail one piece fully, then nail the second piece, checking that the miter remains tight as you work.
6. Match Wavy Ceilings Invisibly. If your ceiling dips or rises noticeably, use a scribe block—a flat piece of scrap wood held against the ceiling—to transfer the ceiling profile to the top of the molding. Run a pencil down the scribe block as you move it along the wall so the pencil traces the ceiling outline on the molding. Cut along that line with a jigsaw or coping saw, then install the molding as normal. The molding bottom stays on the wall studs; the top conforms to the ceiling.
7. Erase Every Nail Head. After all molding is installed and nails are set below the surface, fill each nail hole with paintable wood filler, overfilling slightly so it shrinks flush. Once dry, sand the filled areas lightly with 120-grit sandpaper to blend them smooth. Run your hand along the molding to feel for any ridges or gaps that need attention before primer.
8. Paint Like It's Always Visible. Brush on primer designed for molding and trim, then apply two coats of semigloss or high-gloss paint—it hides dust and is easier to clean than flat. Paint the entire molding, including the back edge where it sits tight to the wall. Crown molding reads as one frame; sloppy paint makes the whole installation look amateur.