Baseboard and trim is one of the best-value upgrades you can make to a room. It is inexpensive material-wise, requires only a few tools, and makes a finished space look genuinely polished. The challenge is in the corners. Getting clean, tight joints on inside corners (where most rooms have four of them) is a skill that takes a little practice, but the right technique makes all the difference.
Baseboard comes in profiles ranging from a simple flat 1x4 board to elaborate stacked assemblies with a cap moulding and a shoe moulding at the bottom. For most weekend projects, a ranch-style or colonial baseboard in 3-1/2 inch height strikes the right balance between visual weight and ease of installation. Taller baseboards (5-1/4 inch or more) suit rooms with higher ceilings but require more precise coping. Crown moulding is measured along its face width, not its actual board width, which can create confusion at the lumber yard. Ask for the face width measurement when ordering.
Finger-jointed pine painted trim is the standard choice for painted rooms. It is affordable, stable, and accepts paint well. MDF trim is even more stable (no grain to telegraph through paint) and slightly less expensive, but it is heavier and the edges must be sealed before painting or they will absorb moisture and swell. Solid hardwood trim is the right choice for stain-grade applications or high-traffic areas. Polyurethane foam trim looks identical to wood once painted and installs with construction adhesive, making it a good option for uneven walls.
Measure the perimeter of the room along the floor, wall to wall. For baseboard, this total linear footage is your starting point. Add 10 to 15 percent for waste from cuts, mistakes, and the occasional split piece. For crown moulding, measure the same perimeter but note that outside corners require extra length for the miters. Rooms with bay windows, fireplaces, or built-ins need their perimeters broken into individual segments and measured separately. Always measure each wall individually rather than calculating from room dimensions. Walls are rarely the exact length you expect once you are standing in the room with a tape measure.
Subtract door openings from your baseboard perimeter (you will not run baseboard across a doorway). However, most doors also require casing trim on both sides and across the top, so measure those separately and add them to your material list. Door casing typically uses about 17 linear feet per door when you account for both sides and the head.
The instinct is to miter inside corners at 45 degrees, matching two pieces that meet in the middle. The problem is that rooms are almost never perfectly square, and a small deviation in the corner angle creates a gap that is difficult to fix. Coping is the professional solution: one piece of trim runs flat into the corner, and the second piece is profile-cut (coped) to fit over the face of the first. A coped joint tightens as the wood expands and contracts seasonally, while a miter joint tends to open up over time. A coping saw or an oscillating multi-tool with a fine-tooth blade does the job.
Outside corners are mitered, not coped. Set your miter saw to 45 degrees and cut each piece so the long points of the miters meet at the outside corner. Check the corner angle with a combination square before cutting. If the corner is more or less than 90 degrees, adjust the miter angle accordingly. A bevel gauge set against the corner gives you the exact angle to split between your two cuts.
Baseboard is nailed through the drywall into the wall studs and into the bottom plate. Use a stud finder to mark stud locations before you start. Drive a 2-inch finish nail at mid-height into each stud, and a second nail near the bottom of the board into the bottom plate. Nail the shoe moulding (if used) into the floor, not into the baseboard. This allows the baseboard to move with seasonal humidity changes without the shoe moulding pulling away from the floor. Set all nail heads just below the surface with a nail set, fill the holes with wood filler, and sand flush before painting.
No floor is perfectly flat and no wall is perfectly plumb. For gaps between the bottom of the baseboard and the floor, a shoe moulding (also called quarter-round) covers the gap and gives the installation a finished look. For gaps at the top of the baseboard where it meets the wall, caulk with a paintable latex caulk, tooled smooth with a wet finger. Do not use silicone caulk on trim. It cannot be painted. For walls that bow outward significantly, scribe the baseboard to follow the wall contour using a compass set to the maximum gap distance, then sand or plane to the scribe line.
Prime all raw trim before installation if you plan to paint it. Primed trim is easier to touch up after nailing than bare wood. Apply two coats of semi-gloss paint, which is durable and easy to wipe clean. Caulk all seams where trim meets the wall and where pieces meet at joints, then paint over the caulk with a small brush. This is what separates a professional-looking result from a DIY one: the caulk fills any minor gaps and the painted-over caulk makes everything look like one continuous surface.
