Trim and Molding Calculator

How to Use This Trim Calculator

Trim is sold by the linear foot and installed by the linear foot, so this tool never asks for square footage. Everything starts from the length of the run you are covering: the perimeter of the room for baseboard, crown and chair rail, or the outline of each opening for casing.

Calculation mode picks where the run comes from. Room dimensions takes the length and width, doubles the sum, and treats the result as the perimeter. That works for a plain rectangular room and it is wrong for anything with a jog, a chase, a closet bump or a bay. Enter linear feet directly is the honest option for an irregular room, and it is the only option for a single wall or a piece of furniture.

Trim type changes how the openings are handled. Baseboard and chair rail stop at a doorway, so the door width comes off the run. Crown molding runs along the ceiling and does not care about doors, so it uses the full perimeter. Casing ignores the perimeter entirely and switches to the outline of each opening: two times the height plus the width, for every door and every window.

Waste factor is the number that decides whether you make one trip or two. Ten percent covers a rectangular room. Push it to 15 for a room with bay windows, arched openings or long crown runs that need a scarf joint in the middle. The waste is mostly offcuts rather than mistakes, which is why a long wall cut from a short stick generates more of it.

Stock length converts your total into sticks. Trim ships in 8, 12, 14 and 16 foot lengths, and the calculator divides the run with waste by your choice and rounds up to a whole stick. The purchased length and the cost both reflect buying whole sticks, which is how the yard sells them. Expect the purchased figure to run above the run with waste, because that leftover half stick is real money.

Wall corner angle sets the miter. A square corner takes 45 degrees per piece, and the calculator halves whatever angle you enter. Set it to 135 for a bay window inside corner and you get 67.5 degrees. The last two outputs report the typical profile width for the trim type you picked and a material cost based on the price per linear foot you entered.

The Six Trim Profiles and Where They Go

A trimmed room is usually a stack of profiles, and each one has a job. Knowing which is which keeps you from buying the wrong width or mounting it at the wrong height.

Home centers stock baseboard in 3-1/4 and 5-1/4 inch heights, which trace back to the nominal 1 by 4 and 1 by 6 boards the profiles were milled from. Crown is sold by its width across the face, and that face width decides the spring angle, the angle at which the molding sits against the wall and ceiling. Crown under about 3-5/8 inches typically has a 45 degree spring angle and the wider profiles usually run 38 degrees. The spring angle matters because it changes the saw setting if you cut crown flat on the table rather than nested against the fence.

Chair rail height deserves its own note. The traditional 32 inches comes from the height of a chair back, and it also lines up with the top of a standard 30 inch counter plus a backsplash. In a dining room with a wainscot below, the chair rail caps the wainscot and the height follows the wainscot panel rather than the chair. Measure before you cut, because moving a rail after the nail holes are filled means patching paint.

Linear Feet, Not Square Feet

The most common estimating error on a trim job is measuring wall area. It feels natural, since paint and drywall both work that way, and it produces a number that has nothing to do with what the yard will sell you. A 12 by 12 room with 8 foot ceilings has 384 square feet of wall and 48 linear feet of baseboard. Only one of those numbers appears on a trim invoice.

Start with the perimeter, then walk the room and adjust. Closets count if they get trimmed, and a closet with a door and three walls adds its own run plus a door deduction. A chase for ductwork or plumbing pushes the baseboard out and back, adding two short runs and, depending on the depth, a corner that needs a miter. A fireplace with a hearth usually breaks the baseboard and leaves two ends that need to be returned into the wall with a small mitered return rather than left hollow.

For casing, measure each opening rather than adding to the perimeter. A 32 by 80 inch door takes two 80 inch legs plus a head across the top, and with the casing sitting proud of the jamb by about 3/8 inch on each side, the head is the door width plus twice that reveal, then plus twice the casing width if you want miters at the top corners. In practice, most carpenters order the head at door width plus 6 to 8 inches and trim the miters to fit. Two doors and three windows on a floor plan come to roughly 70 linear feet of casing, which is a bigger number than most first-time estimators expect.

Finally, note the difference between the run and the purchase. The run is what the room needs. The purchase is what the yard sells, in whole sticks of a fixed length. A 45 foot baseboard run with 10 percent waste is 50 feet of material, and 50 feet in 8 foot sticks is seven sticks, which is 56 feet of trim to carry home. That six foot surplus is the honest answer to "how much do I buy," and it is why buying one extra stick and leaving it unopened is a reasonable plan.

Cutting Angles: Inside, Outside and Coping

Angles are where a trim job succeeds or fails, and there are only three situations. An inside corner, an outside corner, and a splice where two sticks meet along a straight wall.

Inside corners get coped, not mitered. A miter in an inside corner looks fine on the day you install it and opens up over the next heating season, because the two walls move independently and a miter has nothing holding it closed. Coping solves this. Cut the first piece square and run it tight into the corner. Then take the second piece, cut the end at 45 degrees to expose the profile, and use a coping saw to cut along the line where the face meets the back. The result is a joint that looks like a miter but slides as the house moves. It takes about five extra minutes per corner and it is the single biggest difference between amateur and professional trim work.

Outside corners get mitered. Both pieces are cut at half the corner angle and glued as well as nailed, since an outside corner catches every shoulder and vacuum cleaner that comes past it. Glue the miter, nail it, and fill the seam with paintable caulk rather than wood filler, because caulk flexes with the joint instead of cracking out of it.

The formula behind the table is simple: cut each piece at half the measured angle. What makes it hard in the field is that framing is rarely square. A wall framed at 89 degrees instead of 90 will show a gap on the face of a wide crown profile, and even a one degree error is visible over a 5 inch face. Use an angle finder on every corner rather than assuming 90, and always test the setting on a scrap of the actual molding before cutting a full stick. Crown makes this worse, because the profile is cut across a slanted face and the error multiplies.

Splices on long walls. Trim comes in fixed lengths, so a 22 foot wall gets two sticks joined in the middle with a scarf joint, which is a miter cut at a very shallow angle rather than a butt joint. The shallow angle hides the seam because paint bridges it. Set the scarf so the overlap runs away from the most likely viewing direction, and place it over a stud so both pieces have something to nail into. Crown runs over 16 feet almost always need one, which is one more reason to add waste on long walls.

One note on cutting crown. You can cut it nested, sitting at its installed spring angle against the saw fence, in which case the miter is simply half the wall angle and the bevel stays at zero. You can also cut it flat on the saw table, which requires a compound miter with both a miter and a bevel setting that depend on the spring angle. Nested is easier to get right and it is what most carpenters do. If you cut flat, use the compound miter chart that comes with the molding rather than guessing, because both numbers change with every spring angle.

MDF vs Solid Wood vs PVC

The profile you pick matters less than the material you pick it in, because material decides where the trim can go and how it takes a finish.

MDF dominates painted trim for good reasons. It is uniform, so it does not have sap pockets or grain that fights a miter, and its edges machine cleanly. It also expands when it takes on water, which is a real limitation rather than a theoretical one. Baseboard against a slab that wicks moisture will swell at the bottom and the paint will flake off in a band an inch tall. In a bathroom, a basement or anywhere the trim touches concrete, PVC or a moisture-resistant MDF made for the purpose is the safer buy.

Solid wood earns its price when the trim will be stained. Oak and poplar both take stain predictably, and the grain is the point. Pine stains blotchy unless you seal it first with a conditioner, and finger-jointed pine has visible glue joints that read as dark lines under stain even though they disappear under paint. If you are painting, finger-jointed pine and MDF are functionally equivalent and the choice comes down to price and how the material behaves under a nail gun.

One practical note that saves a second trip: buy all your trim for a room at once, from one stack. MDF and wood trim vary slightly in width and profile between production runs, and a stick from a different batch can sit a sixteenth of an inch proud at a splice. That gap is nearly invisible on a shelf and very visible on a continuous run of crown at eye level.

Worked Example: A 12 by 12 Bedroom

Take a 12 by 12 bedroom with one 32 by 80 inch door, one 3 by 4 foot window, and a plan to install painted MDF baseboard and crown.

The perimeter is 2 times 12 plus 12, which is 48 feet. Baseboard stops at the door, so deduct the 3 foot door width and the run is 45 linear feet. Crown runs along the ceiling and takes the full 48 feet, with no deduction for either opening. At a 10 percent waste factor that is 50 feet of baseboard material and 53 feet of crown.

Baseboard in 8 foot sticks is 7 sticks, or 56 feet to carry home, and crown is 7 sticks as well. If you prefer 16 foot sticks, baseboard is 4 sticks and crown is 4 sticks, which cuts the offcut pile but means wrestling a 16 foot bundle up a stairwell.

Casing is a separate purchase. The door outline is two 80 inch legs plus a 36 inch head, which is 196 inches or about 16.3 linear feet. The window is two 4 foot legs plus a 3 foot head, which is 11 feet. Together that is 27.3 feet, and with 15 percent waste for the eight mitered corners, about 32 feet of casing, or four 8 foot sticks.

Material cost at $2.50 per linear foot for painted MDF: baseboard and crown come to about $270 in purchased sticks, and casing adds roughly $80. Trim is one of the few finish trades where the material is cheap and the labor is not. A trim carpenter at $3 to $8 per linear foot installed would charge $400 to $1,000 for this room, which is why so many homeowners run baseboard themselves and hire out only the crown.

Count the corners before you buy. A plain rectangular bedroom has four inside corners at the floor and four at the ceiling, plus two outside corners if the door casing wraps into the room, which is 10 joints and about 10 inches of waste from mitered offcuts. A room with a closet, a jog and a bay window can easily double that, which is where the 15 percent waste factor starts to look conservative rather than cautious.

5 Mistakes That Leave Gaps at the Corners

1. Mitering inside corners. A mitered inside corner looks tight on install day and opens within a heating season, because the two walls move independently. Cope the inside corners. Cut one piece square into the corner, then coping-saw the profile of the mating piece. It is slower and it is the difference between a joint that lasts and one that needs caulk every year.
2. Assuming every corner is 90 degrees. Framing is rarely square, and one degree of error shows on a wide crown profile. Measure each corner with an angle finder, cut test pieces from scrap, and adjust before committing a full stick. Do not trust the framing to be straight either, since a bowed stud pushes baseboard off the wall and opens the joint at the next corner.
3. Buying material after the first trip. Trim from a different production run can differ in width by a sixteenth of an inch, and a mismatch at a splice is obvious on a continuous crown run. Buy everything for the room at once from one stack, and keep the receipt for the unopened spare stick.
4. Using wood filler on outside corners. Wood filler dries hard and cracks out of a miter that moves with seasonal humidity. Paintable caulk flexes with the joint and stays put. Save the filler for nail holes, where nothing moves.
5. Skipping the caulk line at the wall. Even a well-installed baseboard leaves a hairline gap where it meets the wall, because neither the wall nor the trim is perfectly flat. A thin bead of paintable caulk along the top edge, tooled with a finger, turns a visible shadow line into a crisp edge. It is the last five minutes of the job and it is the step that makes amateur trim look professional.