Things You'll Need
Installed around the perimeter, baseboard meets inside and outside corners. The miter angle remains the same for both types of corners but the position of the baseboard changes. Cutting baseboard requires minimal woodworking skills.
Measure the length of the wall where you wish to place the baseboard. Mark the measurement on the baseboard. If the length includes a corner, set the blade of a miter saw at 45 degrees.
Don safety glasses and a dust mask. Place the baseboard on the miter-saw bed, standing on edge with the back flush against the fence. Position the baseboard to cut off the face or profile if you are cutting an inside corner. Position the baseboard to cut off the back if you are cutting an outside corner. Hold the baseboard tight against the fence with one hand.
Grasp the handle of the saw with the other hand. Turn on the saw and trim the baseboard 2 inches longer than the measurement.
Measure from the longest point or the sharp point of the miter and mark the baseboard at the measurement needed for the wall. Set the blade at 90 degrees if the baseboard terminates against a flat wall. If the other end of the molding terminates at another corner, swing the blade to the left or right as needed to trim off the profile for an inside corner, or off the back for an outside corner.
Place the baseboard against the wall as if it were installed and test the fit. Trim 1/16 inch from one end if it's too tight and test again until it fits snugly but is not too tight. Remove the baseboard from the wall.
Measuring and cut the next piece to the left or right as needed. Test-fit and begin installing the baseboard when you have two or more pieces that fit together.
Don safety glasses. Place the baseboard between the two horizontal guides on the manual miter saw. There are three corresponding slots on both sides for the saw blade. One set of slots cuts molding at 90 degrees. One set cuts at 45 degrees for a left-hand miter. One set cuts at 45 degrees for a right-hand miter.
Place the baseboard inside the box with its face against the guide nearest your body for an outside corner. Place the baseboard with its back against the fence for an inside corner.
Place the saw in corresponding, 45-degree slots on the left or right. Hold the saw blade up 1/16 inch higher than the top of the molding.
Slide the baseboard to the left or right to align it with the blade at the point where you wish to cut it. Clamp the molding to the guide or use your free hand to hold it. Cut off the molding with the saw.
Remove the saw from the guides. Place an identical piece of baseboard between the guides, aligned like the first piece. Place the saw in the opposite 45-degree slots and cut off the opposing miter angle.
Walls and floors often are out of square. If mitered corners don't fit or have gaps, adjust the blade one or two degrees at a time and trim again. Cut and test-fit scrap pieces if you have doubts about the walls or floor. In some instances for inside corners, a technique known as coping can make miter joints fit better. Coping involves trimming a bit from the mitered end with a small, handheld saw.