Trim & Crown Molding Calculator
Linear feet for trim plus crown compound miter and bevel angles — where neither number is 45 and the profile name misleads you.
Materials
Every profile, this corner
Neither number is 45
Crown cut lying flat needs a mitre and a bevel, and neither is 45°. For the common 38° profile in a square corner they're 31.62° and 33.86°. Setting 45 — which is what an inside corner obviously wants — leaves a gap no amount of caulk hides, because the two faces aren't meeting on the same plane at all.
And the spring angle name is ambiguous in a way that punishes you quietly. Crown is sold as "38°" or "45°", meaning the angle between its back and the wall. The compound formulas want the angle from the ceiling — the complement. Feed 38 in where 52 belongs and you get 38.24° and 25.81°, which isn't nonsense: it's the correct answer for 52° crown. Two plausible numbers, both wrong for the moulding in your hand. The trap is invisible on 45° crown, because 45 is its own complement — which is exactly why nobody meets the problem until they buy 38.
The old method avoids all of it. Nest the crown upside down against the fence at its spring angle, the way it sits on the wall, and the cut is a plain 45° mitre with no bevel. The saw does no compound work because the moulding is already holding the angle. Slower to set up, far harder to get wrong, and it stays inside the saw's range at corners where the compound angles don't.
- Cope the inside corners. A mitre relies on the wall being exactly square and staying that way; a coped joint has one piece running through and the other scribed to it, so it closes rather than opens as the house moves.
- Measure every corner. Almost no room is square, and crown magnifies the error — a corner 2° out shifts the mitre about a degree and shows as a line at the ceiling.
- Wide corners exceed the saw. Past about 120° the mitre climbs sharply — a 135° corner needs 56°, beyond most compound saws. Nest it instead.
- Crown doesn't stop at doorways. It runs the full perimeter; only baseboard deducts the openings.
- Cut test pairs from offcuts, for every distinct corner rather than once for the room. Saw scales aren't accurate to the tenth of a degree these figures are quoted in.
How to use
- Pick the trim type and enter the room size.
- For crown, identify the profile by measuring it rather than trusting the label.
- Measure the actual corner angle — almost no room is square.
- Cut a test pair from offcuts before touching a full length.
Frequently asked questions
What angle do I cut crown molding at?
Cut lying flat on a compound saw, a square corner in the common 38 degree profile needs a 31.62 degree miter and a 33.86 degree bevel. Neither is 45. Setting 45 — which is what an inside corner appears to want — leaves a gap that no amount of caulk hides, because the two cut faces are not meeting on the same plane at all.
What are the angles for 45 degree crown?
A 35.26 degree miter and an exactly 30 degree bevel, for a square corner cut flat. It is the profile people learn on, partly because that round 30 sticks in the memory and partly because it is symmetrical — its wall and ceiling angles are both 45, so the naming ambiguity that ruins 38 degree crown cannot bite.
Why did my crown angles come out wrong?
Almost certainly the spring angle convention. Crown is sold as 38 degree or 45 degree, meaning the angle between its back and the WALL — but the compound formulas want the angle from the CEILING, which is the complement. Feed 38 in where 52 belongs and you get 38.24 and 25.81 degrees, which is not nonsense: it is the correct answer for 52 degree crown. Two plausible numbers, both wrong for the moulding in your hand.
What is the spring angle?
The angle the moulding sits at between wall and ceiling. Hold a square against the back of the piece and you will find two flats — one bears on the wall and one on the ceiling — and the spring angle is the angle between them and their surfaces. The safest habit is to measure both rather than trusting the label, because the two numbers are complements and the label only ever quotes one of them.
What is the nested method?
Cutting the crown upside down against the fence, held at its spring angle the way it sits on the wall. Done that way the cut is a plain 45 degree miter for a square corner with no bevel at all, because the moulding is holding the angle rather than the saw. It is slower to set up and considerably harder to get wrong, which is why it has outlived several generations of saw.
Which method is better?
Nesting, for most people and most rooms. It uses one saw setting rather than two, it removes the spring angle convention from the problem entirely, and it stays within the saw’s range at corners where the compound angles do not. Cutting flat is faster once set up and is the only option on very wide crown that will not fit nested, so it earns its place on big jobs.
Can my saw cut any corner?
No, and wide corners run out of range faster than people expect. A 135 degree corner in 38 degree crown needs a 56 degree miter, beyond the roughly 50 degrees a typical compound saw reaches. The miter climbs sharply past about 120 degrees. Nesting the moulding sidesteps this — the nested miter falls as the corner opens up, so it stays comfortable exactly where the compound angles do not.
Should I miter or cope inside corners?
Cope them. A mitred inside corner is two cuts relying on the wall being exactly square and staying that way, and it opens as the house moves and the timber shrinks. A coped joint has one piece running through and the other scribed to its profile, so seasonal movement closes it rather than opening it. Outside corners have to be mitred, since coping is not an option there.
Do I need to measure every corner?
Yes, and crown is where it matters most. Almost no room is truly square, and the compound angles change faster than the corner does, so a corner two degrees out shifts the miter by about a degree and shows as a visible line at the ceiling. A digital angle finder costs very little against a room of crown, and it turns guesswork into arithmetic.
How much waste should I allow?
Around fifteen per cent for crown and ten for baseboard. Crown deserves more because every corner is a compound cut and the first one of each type is effectively a test piece — cut those from offcuts you already have rather than from a fresh length. Casing is closer to crown than baseboard, because mitred returns leave offcuts that are rarely reusable.
Does crown stop at doorways?
No — it runs the full perimeter at the ceiling, so nothing is deducted for openings. Only baseboard stops at the doors. It is an easy thing to get backwards when working from one perimeter figure for the whole room, and it is the difference between having enough material and being one length short at the end of the day.
How accurate are these angles?
The arithmetic is exact, and it is more precise than any saw scale. Miter scales are rarely trustworthy to the tenth of a degree these figures are quoted in, and the timber itself is not perfectly straight. Use the numbers to get to within a fraction of a degree, then cut a test pair from offcuts for each distinct corner and adjust from what you see.
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