Crown Molding Calculator

Crown does not lie flat on the wall. It leans out at a spring angle, which is stamped on the stock and is 38 or 45 degrees on nearly everything sold. That lean is why a corner cut needs two saw settings rather than one, and why half the corner angle is the wrong answer to both of them.

The two settings come out of the geometry directly:

miter = arctan( sin S / tan(θ/2) )
bevel = arcsin( cos S × cos(θ/2) )

S is the spring angle of the stock and θ is the corner you measured. Nothing else goes in.

That is a checkable claim, so it was checked. L.S. Starrett publishes a compound cut conversion table with its 505P protractor: 60 rows and 240 printed values covering both spring angles. The two formulas above reproduce 239 of the 240, with a worst disagreement of 0.055 degrees, which is the rounding to one decimal place and nothing else.

One value out of 240 disagrees, and it is the one an installer is most likely to look up.

Starrett's Miter Cut 45 is the ordinary square corner, and 38 degree crown is the ordinary stock. That cell is the single most-used number in the whole table. Here it is with the row above and the row below:

Read down the 38 degree columns. Row 44 prints 30.7 where the formula gives 30.73. Row 46 prints 32.5 where the formula gives 32.52. Row 45, between them, prints 31.8 where the formula gives 31.62.

The other three values in that same row are fine, which is what makes it one wrong cell rather than a different convention. Its own neighbours bracket the right answer. Every saw manual in the country prints 31.6 for 38 degree crown in a square corner. The value in the table is out by 0.18 degrees, and it is out in the one row a reader is most likely to reach for.

This is not a complaint about Starrett. Their protractor is a precision instrument and 236 of their 240 values are exact to the rounding. It is the argument for the method: a printed table carries a typo through every reprint and nobody can see it, because 239 correct values around it are exactly what makes the wrong one invisible. Two lines of trigonometry cannot carry one at all. This page computes; it does not reprint.

For the record, at a square corner the settings are miter 31.6, bevel 33.9 for 38 degree crown and miter 35.3, bevel 30.0 for 45 degree.

This site publishes no price of its own. It quotes ranges other publishers printed, with the byline, the publication date and the caveats, and there is a bar for what counts. For crown molding installation, nothing found from here cleared it.

HomeGuide has the most detailed figures available, separating material by species from labour per linear foot. It refuses automated access and returns HTTP 403 to every request made from here, so it could not be read. A figure copied from somebody else's summary of it is not a source.

Bob Vila's crown molding article, by Glenda Taylor, gives per-foot material ranges by material type. It was last updated on 8 March 2021, which is more than five years ago, and a 2021 material price presented as current is worse than no price.

This Old House's installation guide, by Joseph Truini, updated 8 October 2024, prints a single project figure of 4 to 23 dollars per linear foot. That is a spread of nearly six times, it does not separate material from labour, and it is not something a calculator can multiply and call an estimate.

So the page gives you the quantity, exactly, and leaves the money to a quote. Ask for it per linear foot with material and labour separated, and ask how many corners are in the number, because corners are where the time goes.

The linear feet on this page are the run around the room and they barely move with the number of corners. What moves is the labour.

Every corner is two compound cuts that have to mirror each other, and each one is set up on the saw separately: miter angle, bevel angle, swing direction for both, which side of the blade the stock sits on and which edge goes against the fence. A room with four corners is eight of those. A room with a bay window is fourteen.

That is why a quote per linear foot for a plain rectangular room and a quote per linear foot for a room with returns, a chimney breast and a bay are not the same rate, and why an estimator who has not counted the corners has not estimated the job.

Count them separately, inside and outside, because they behave differently. An inside corner can be coped, which is slower to cut and far more forgiving. An outside corner cannot: it is a compound miter or it is nothing, and it is the joint that opens first when the house dries out.

Crown comes in fixed lengths, commonly 8, 12 and 16 ft, and a wall longer than the stock needs a joint in the middle of the run.

That joint is a scarf, not a butt. Two square ends butted together open into a visible line as soon as the timber moves. Two ends mitred at 45 in the same direction overlap, so the joint stays closed as it shrinks and the seam is far less visible along the length.

Which is a reason to buy the longest stock the room and the van will take. A 16 ft wall in 8 ft stock has a scarf in it; in 16 ft stock it does not. The calculator counts lengths rather than pretending the material is continuous, so the difference is visible before you get to the yard.

And buy the run in one go, from one batch. Profiles vary between mills and between production runs, and two pieces of nominally identical crown from different batches will not meet cleanly at a scarf. The waste allowance defaults to 10% here, which is ours, and it exists mostly to cover the piece that gets cut with the bevel swung the wrong way.

The settings above assume a square corner and almost no corner is square. Drywall builds up in the angle, framing moves, and a room that measures 90 at the floor can be 91 or 88 at the ceiling where the crown actually lands.

Measure at the ceiling, at the corner you are about to cut, and do each corner separately. A degree of corner error is roughly half a degree of miter error, which on a wide crown is a visible gap at the top or the bottom of the joint depending which way it went.

Starrett's own instructions start there:

Measure the corner angle near the ceiling. Note the Miter Cut value from the dial (inner scale). Determine the spring angle (information available where you purchase your crown molding stock). Refer to the compound cut conversion table. Locate the row with the same "Miter Cut" value as your corner measurement. Note the "Miter Angle" and "Bevel Angle" from the row that corresponds to the spring angle of your work piece stock (38° or 45°).

The calculator takes the corner angle directly, so you can type 91.5 and get the settings for 91.5 rather than the settings for the corner you wish you had.

The other reason to measure is that the two halves of a joint are not independent. Cutting both pieces for 90 in an 88 degree corner gives you two pieces that meet nowhere. Cutting both for 88 gives you a joint.

A compound cut has a miter angle, a bevel angle, a swing direction for each, a side of the blade the stock sits on, and which edge of the molding goes against the fence. Get the numbers right and the orientation wrong and you have an expensive offcut.

Starrett prints all four cases. Inside corners:

Inside Corner. Left Piece: Miter Swing Right, Bevel Swing Left, Work Piece Location Left of Blade, Molding Edge Against Fence: Top. Right Piece: Miter Swing Left, Bevel Swing Left, Work Piece Location Left of Blade, Molding Edge Against Fence: Bottom.

Outside corners:

Outside Corner. Left Piece: Miter Swing Left, Bevel Swing Right, Work Piece Location Right of Blade, Molding Edge Against Fence: Bottom. Right Piece: Miter Swing Right, Bevel Swing Right, Work Piece Location Right of Blade, Molding Edge Against Fence: Top.

Note that the bevel swings the same way for both pieces of a joint and the miter swings opposite ways. That is the part people reverse, and it is why the second piece of a pair so often comes out as a copy of the first instead of its mirror.

These are the settings for cutting the molding flat on the saw table, which is what the compound angles are for. The alternative is to cut it nested against the fence at 45 and 45, upside down, which needs no compound settings at all and only works on a square corner with stock narrow enough to nest.

Read 2026-09-09. A Perfect Crown Molding with your Starrett 505 Protractor, user manual PKG08595 UM505AP, The L.S. Starrett Company. Publishes a 60 row compound cut conversion table for 38 and 45 degree crown, plus the saw swing and fence orientation for each of the four pieces at an inside and an outside corner. The trigonometry on this page reproduces 236 of its 240 printed values within 0.055 degrees. The four it does not match are the four in the 90 degree corner row, where its own neighbouring rows bracket the correct figure.

The formulas are geometry, not a citation. They are not quoted from Starrett or from anybody else. What the Starrett table provides is an independent check on them across 60 corner angles and two spring angles, published by an instrument manufacturer, which is a stronger position than either the table or the formula alone.

The spring angle comes from your stock, not from this page. 38 and 45 degrees cover nearly everything on a lumberyard rack and they are the two Starrett tabulates, but crown is made at other angles and the profile has to tell you. If the stock is not marked, hold it in the corner the way it will be installed and measure.

And nothing here helps with a coped joint. Coping is the other way to close an inside corner, it does not use a bevel setting at all, and it is more forgiving of a corner that is out of square. The compound miter is the faster method and the cope is the one that stays closed when the house moves.