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Crown Molding Calculator
Use this free crown molding calculator to work out exactly how much molding to buy before you go to the store. Enter the room size or the total wall length, pick the molding size and material, add your inside and outside corners, and choose a waste allowance. The calculator gives you the linear feet needed, the number of pieces to buy in 8, 12, or 16 foot lengths, and an estimated material cost, so you buy enough the first time and do not end up short with one wall unfinished.
| Item | Amount |
|---|---|
| Wall length (perimeter) | 52 ft |
| Waste (10%) | 5.2 ft |
| Total molding needed | 57.2 ft |
| Pieces to buy | 8 × 8 ft |
| Estimated material cost | $82 – $164 |
How it works
The calculator starts with the wall length the molding must cover. For a rectangular room that is the perimeter: twice the length plus twice the width. A 12 by 14 foot room has a perimeter of 2 × 12 + 2 × 14 = 52 feet. If your room is not a rectangle, measure each wall separately with a tape measure and add them up, or use the total wall length mode and type the sum in directly. Measure along the wall at ceiling height, and include the full length of every wall, even where a door or window interrupts it, because the molding runs across the top of the opening too. If a wall has a fireplace, a built-in, or an opening with no wall above it, subtract that section.
Next it adds the waste allowance. Crown molding is cut at 45-degree miters at every corner, and every cut creates an offcut that is often too short to use elsewhere. Ten percent is the standard allowance for a rectangular room with four inside corners. If your room has bay windows, angled walls, or several outside corners, choose 15 percent, and if you are installing crown molding for the first time, 15 to 20 percent is the safe choice, because a miscut miter is the most common beginner mistake and a spare piece saves a second trip to the store. The calculator also counts your corners: if you enter more than six corners in total, it suggests stepping up to 15 percent waste.
The piece count is the total needed divided by the piece length, always rounded up. You cannot buy part of a piece, so a 57.2 foot need in 8 foot pieces is 57.2 ÷ 8 = 7.15, rounded up to 8 pieces, which is 64 feet of molding bought. Longer pieces mean fewer joints along a long wall, and fewer joints look better, so if any wall is longer than 12 feet, 16 foot pieces are worth considering when you can transport them. A 16 foot piece does not fit in most cars, so check your vehicle or the store's delivery before choosing them.
Material prices are typical per linear foot ranges, and the size of the profile adjusts them: a 3.5 inch profile costs about 15 percent more than a 2.5 inch one, a 5.5 inch profile about 50 percent more, and a 7.25 inch profile about 80 percent more, because wider molding uses more material. MDF is the cheapest option at about $1.25–$2.50 per linear foot and paints smoothly, but it is heavy and does not hold up to moisture. Pine runs about $2–$4 and takes stain or paint. Polyurethane, at about $3–$6, is light, flexible enough for slightly curved walls, and will not rot. Hardwood such as oak or maple runs about $4–$9 and is the choice when the molding will be stained to match wood trim. Installation by a professional typically adds about $5–$12 per linear foot on top of the material, and that is not included in the estimate here.
Choosing the right size matters as much as the length. The classic rule is that the molding height should be about one inch for every foot of ceiling height up to 8 feet, so a 3.5 inch profile suits a standard 8 foot ceiling, while 9 and 10 foot ceilings call for 5.5 inches and taller ceilings for 7.25 inches. A profile that is too large for a low ceiling makes the room feel cramped, and a small profile on a tall ceiling looks lost. If you are matching existing trim in the house, measure that profile and pick the closest size.
Needed = perimeter × (1 + waste %)
Pieces = needed ÷ piece length, rounded up
Worked example
You are adding crown molding to a 12 by 14 foot bedroom with 8 foot ceilings. The room has four inside corners and no outside corners. You choose a standard 3.5 inch MDF profile, 8 foot pieces, and a 10 percent waste allowance.
Step 1: Perimeter — 2 × (12 + 14) = 52 feet of wall.
Step 2: Waste — 52 × 10% = 5.2 feet.
Step 3: Total needed — 52 + 5.2 = 57.2 linear feet.
Step 4: Pieces — 57.2 ÷ 8 = 7.15, rounded up to 8 pieces of 8 feet, which is 64 feet bought.
Step 5: Cost — MDF at $1.25–$2.50 per foot, adjusted by 1.15 for the 3.5 inch size, is $1.44–$2.88 per foot. For 57.2 feet that is 57.2 × $1.44 = $82 at the low end and 57.2 × $2.88 = $164 at the high end.
The answer is 57.2 linear feet needed, 8 pieces of 8 feet to buy, and an estimated material cost of $82–$164. If you switch to 16 foot pieces, you need 57.2 ÷ 16 = 3.58, rounded up to 4 pieces, which is also 64 feet bought, with only three joints instead of seven.
FAQ
How much crown molding do I need for a room?
Add up the length of every wall the molding will run along, which for a rectangular room is the perimeter, 2 times length plus width. Then add a waste allowance of 10 percent for a simple rectangular room, or 15 percent if the room has many corners, angles, or long runs that need joints. A 12 by 14 foot room has a 52 foot perimeter, and with 10 percent waste you need 57.2 linear feet.
What is the standard waste percentage for crown molding?
Ten percent is the standard waste allowance for a rectangular room with four inside corners, because every corner is a mitered cut and some offcuts are too short to reuse. Use 15 percent for rooms with bay windows, angled walls, or many outside corners, and 15 to 20 percent if you are installing crown molding for the first time, since miscut miters are common while you learn.
What length does crown molding come in?
Crown molding is commonly sold in 8 foot, 12 foot, and 16 foot lengths, and some suppliers stock other lengths. Longer pieces cost more per foot but mean fewer joints along a long wall, and fewer joints look better, so 16 foot pieces are the best choice for walls longer than 12 feet when you can transport them. Always check the actual lengths your supplier stocks before you buy.
How much does crown molding cost per linear foot?
Material prices vary by material and size, but typical ranges are about 1.25 to 2.50 dollars per linear foot for MDF, 2 to 4 dollars for pine, 3 to 6 dollars for polyurethane, and 4 to 9 dollars for hardwood such as oak or maple. Larger profiles cost more than small ones. Installation by a professional typically adds about 5 to 12 dollars per linear foot on top of the material.
Do inside and outside corners need extra molding?
Corners do not add length to the wall measurement, because the molding runs the full length of each wall and meets at the corner. What corners do add is cuts, and every cut risks a miscut and creates an offcut, so rooms with many corners need a higher waste percentage. That is why this calculator asks for your inside and outside corner counts and suggests 15 percent waste when the total is high.