Crown Molding Calculator

Calculate how many linear feet of crown molding a room needs and how many 8, 12 or 16 ft pieces to buy, with inside and outside corner counts, finish nails and cost.

By CalcBuilt Editorial TeamUpdated September 11, 2026Formulas checked against manufacturer specs, see how we calculate.

Quick answer: To find how much crown molding you need, add up the room perimeter and any extra runs, then add 10% for waste and divide by the piece length. A 12 x 14 ft room has a 52 ft perimeter, which is 57.2 ft of crown molding with 10% waste, or 4 pieces of 16 ft.

Your measurements

A length built from stock pieces: total length divided by piece length, rounded up, with the last piece cut.

Room lengthftRoom widthftExtra runsftBump-outs, soffits, closets or a second room sharing the same molding.Piece length16 ft spans most walls with no scarf joint but does not ride in a pickup; 12 ft is the longest most yards stock in solid wood. Any wall longer than the piece needs a scarf joint.Inside cornersA rectangular room has 4. Each is coped, and each cope scraps 6 to 12 in, which is where the waste goes.Outside cornersAround a chimney breast, soffit or bump-out. Each is mitered at half the true angle; corner bead makes most outside corners 91 to 93 degrees, not 90.Waste allowance%10% for a simple room, 15% with many corners or a ceiling that is out of square. Cut trim is not returnable, so add one spare piece for a botched cope.Price per linear ft (optional)Entered per foot in both unit systems. Typically (2026) primed MDF crown is $1.50 to $3 per ft, finger-joint pine $2 to $4, solid poplar or oak $4 to $8.

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Crown molding needed52 ftAll results

Results

Crown molding needed: 52 ft; 52 ft room perimeter plus 0 ft of extra runs. 57.2 ft with 10% waste.
Pieces to buy: 4 pieces of 16 ft; 64 ft purchased. Add one spare piece for a botched cope; cut trim is not returnable
Corner cuts: 4 corners; 4 inside corners to cope, 0 outside corners to miter
Finish nails: 78 nails; Two 2 to 2.5 in (5 to 6 cm) 15 or 16 gauge nails every 16 in, one into the wall and one into the ceiling framing

Crown Molding formula

Linear feet = 2 x (Room length + Room width) + extra runs
Order length = Linear feet x (1 + waste %)
Pieces = Order length / piece length, rounded up
Nails = Linear feet x 12 / 16 x 2

Worked example

A 16 x 20 ft living room with a 5 ft soffit run, six inside corners and two outside corners, using 12 ft pieces with 15% waste: perimeter = 2 x (16 + 20) = 72 ft, plus 5 ft = 77 ft. With waste: 77 x 1.15 = 88.55 ft. 88.55 / 12 = 7.4, so buy 8 pieces of 12 ft, which is 96 ft of molding.

Nails: 77 x 12 / 16 = 57.75, rounded up to 58 nailing points, times 2 = 116 finish nails. At $3.50 per foot the 96 ft purchased costs $336.

Quick reference

Crown molding for common room sizes with 10% waste
Room	Perimeter	With 10% waste	16 ft pieces	8 ft pieces
10 x 10 ft	40 ft	44 ft	3	6
10 x 12 ft	44 ft	48.4 ft	4	7
12 x 12 ft	48 ft	52.8 ft	4	7
12 x 14 ft	52 ft	57.2 ft	4	8
14 x 16 ft	60 ft	66 ft	5	9
16 x 20 ft	72 ft	79.2 ft	5	10
20 x 20 ft	80 ft	88 ft	6	11

Coping vs mitering corners

Outside corners are mitered, and rooms are never square: drywall corner bead builds most outside corners to 91 to 93 degrees. Measure with a digital angle finder, cut half the angle on each piece, test on two scraps, then glue the miter and cross-pin it with 23 gauge pins. Inside corners are coped. The first piece runs square into the corner; the second is cut at 45 degrees, the profile is traced along the miter line with a coping saw and back-cut so only a thin edge touches. A coped joint hides a corner that is out of square and stays closed as the wood moves through the seasons, where a mitered inside corner opens up.

Plan the order so you cope toward the door. Start with the wall opposite the entry, cut square on both ends, then work around the room so each piece is coped on one end. A wall longer than the stock piece gets a 45 degree scarf joint over a stud, glued and pinned, never a butt joint. 16 ft MDF flexes enough to need two people and will not ride in a pickup; the yard delivers it, typically $50 to $100.

Spring angle and saw settings

Crown does not sit flat on the wall; it leans out at its spring angle, 38 degrees (labeled 38/52) or 45 degrees (45/45). Set a piece in a framing square: on 38 degree crown the wall leg is longer than the ceiling leg. Cutting nested, upside down against the fence at the angle it sits on the wall, uses a plain 45 degree miter. That works up to about 4-1/2 in crown on a 10 in saw and 5-1/4 in on a 12 in; bigger crown is cut flat with compound settings, 31.6 degrees miter and 33.9 degrees bevel for 38 degree crown, 35.3 and 30 for 45 degree crown.

Nail into the wall studs and the ceiling joists, or, where the joists run parallel to the wall, into a beveled backer strip screwed to the top plate; mark all of them before the first piece goes up. Two 2 in 15 or 16 gauge nails every 16 in is the pattern. Prime and first-coat on sawhorses before install, and prime MDF cut ends so they do not swell. On the wall, fill nail holes, caulk the top and bottom edges and put on the final coat.

What this calculator leaves out

Backer strips (a 2x4 ripped at the spring angle), wood glue and 23 gauge pins for the miters. Paintable caulk at about one 10 oz tube per 40 ft of crown for both edges, filler, primer and paint. Corner blocks are an alternative to coping for a first job. The spare piece for a botched cope and delivery of 16 ft stock are extra.

Mistakes that cost money

Cutting 38 degree crown with 45 degree settings leaves a corner gap no caulk hides; check the spring angle against a square first.
Mitering inside corners at 45 in a room that is 91 degrees opens 1/8 in by the first winter; cope inside corners.
Nailing only into drywall between studs lets the crown sag; mark studs and joists first and add a beveled backer where joists run parallel.
Butt-joining two pieces on a long wall shows a line every season; cut a 45 degree scarf over a stud, glue it and sand.
Painting after install means cutting in two edges on a ladder; prime and first-coat on sawhorses, then fill, caulk and final-coat on the wall.
Buying exactly 4 pieces for 4 walls leaves nothing for a botched cope; add one piece, since cut trim is not returnable.

Key facts

Crown molding is sold in 8, 12 and 16 ft lengths; a 16 ft piece spans most walls without a scarf joint.
Most crown has a 38 or 45 degree spring angle, the angle the molding leans off the wall, and the two need different saw settings.
For 38 degree crown cut flat on the saw, a square inside corner takes a 31.6 degree miter and a 33.9 degree bevel; 45 degree crown takes 35.3 and 30.
A 3-5/8 in crown suits an 8 ft ceiling; 4-1/2 to 5-1/4 in looks right at 9 to 10 ft.
Inside corners are usually coped rather than mitered because a coped joint stays tight when the wood shrinks or the corner is not 90 degrees.

Frequently asked questions

Should I paint crown molding before or after installing it?

Prime and put the first coat on before install, on sawhorses, where it takes minutes a piece instead of a ladder and two cut-in edges. After install, fill the nail holes, caulk the top and bottom edges and put on the final coat. Prime MDF cut ends or they swell. Stain-grade crown is finished before install and the coped corners touched up with a matching marker.

Should I cope or miter crown molding?

Miter outside corners and cope inside corners. Coping takes longer to learn but stays tight when the room is out of square and when the wood shrinks in winter, which a mitered inside corner does not.

What size crown molding should I use?

About 3-5/8 in for a standard 8 ft ceiling, 4-1/2 to 5-1/4 in for 9 to 10 ft ceilings, and larger built-up profiles above that. Very tall crown on a low ceiling makes a room feel shorter.

What angle do I cut crown molding at?

Nested upside down in the saw, a square corner is a plain 45 degree miter. Cut flat, 38 degree spring crown needs a 31.6 degree miter with a 33.9 degree bevel, and 45 degree crown needs 35.3 and 30.

Sources and references

Crown moulding sizes and dimensions guide (Metrie)
How to measure for crown moulding: size, angles and corners (Metrie)
How to cut crown moulding: miter and cope techniques (Metrie)
21/32 x 4-1/4 in x 16 ft primed MDF crown product page (Metrie)

Next steps for this project

The usual order for a paint & walls project. See all paint & walls calculators.

Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.