How to measure crown molding before you cut

Crown molding installation requires three steps: measuring, cutting and nailing. Measuring, most installers agree, is the most important. Here is how to measure crown molding before you cut.

The carpenter’s Golden Rule − “Measure twice, cut once” − is critical for a crown molding job, but taking those measurements in two steps will help ensure that you have enough, but not too much, material to go around.

How much to buy

Before measuring the walls, locate the studs with a stud finder and mark the wall as a guide for where to nail. Use a tape measure to measure each wall from corner to corner to figure the quantity of molding needed.

Many carpenters suggest rounding measurements up to the next foot. For example, for a wall that is 8 feet 3 inches, buy 9 feet of molding.

If the room has inside corners only − like the intersections of the four sides of the interior of a box − add the measurements of the four walls together. Then choose molding lengths that feel most comfortable to work with.

When measuring corners, calculate the length needed to cut the shortest side of the molding. For an inside corner, the top of the molding will be shorter, but for an outside corner, the bottom is shorter.

Molding typically comes in 8-foot lengths, but lumber yards stock 10- or 12-foot lengths. Some lumber dealers advise contractors to work with pieces that run the full length of the wall because that reduces the number of joints and saves installation time.

Divide the total measurement by the length of the molding. Even though you rounded up, add another 10 percent to the total to accommodate bad cuts. That’s how many pieces of trim you’ll need for the job.

If the room has outside corners − like the corners on the exterior of a box − count them. Measure the width of the molding, and multiply that number by the number of outside corners. Then multiply by two. That’s how much extra material you need to account for the corners.

To measure crown molding, some installers recommend calculating inches rather than linear feet.

How to set up precise cuts

Once you have the molding, measure the walls again, from corner to corner, but this time, with even more precision. Then, measure the trim pieces so they match the wall spans exactly.

There are several measuring tools for this high-precision job. Some Pros rely on tape measures, either asking a partner to help out by holding one end or lightly nailing one end to the wall. Others, however, prefer to use the molding itself as a measuring tool, placing it flat against the wall and marking it with a pencil at the point where it needs cutting.

Still others use a level or a framing square. However, make sure the level is not out of alignment or the framing square isn’t bent, which will throw off the measurement.

When measuring for a chair rail, every piece of trim has to be precisely the same height. A measuring tool that works is the story pole made from a piece of lumber or trim. Using the pole as a guide, mark the wall at multiple locations.

When you measure crown molding, test your measuring tool before relying on it to serve up precise measurements. No matter which tool works best for the job, use it consistently so each board and each wall is measured the same way.

Finally, make a cut list − a record of the measurements of each wall, from corner to corner, including whether the piece will finish at an inside or an outside corner, and whether it needs a straight or angled cut.

−By Sharon O’Malley

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