# Crown Molding Miter Calculator

> Computes the saw settings for cutting crown molding flat on a compound miter saw from the wall corner angle and the molding's spring angle: miter = atan(sin(spring) / tan(corner/2)) and bevel = asin(cos(spring) × cos(corner/2)), plus the miter setting for cutting the molding nested (upside-down against the fence) and which end of each piece to keep.

- Calculator id: `crown-molding-miter` · Category: Construction & Home (`construction`) · Tool name: `calculate_crown_molding_angles`
- Canonical page: https://tttkmbb.com/construction/crown-molding-miter · This document: https://tttkmbb.com/construction/crown-molding-miter.md · JSON definition: https://tttkmbb.com/construction/crown-molding-miter.json

## Purpose

Computes the saw settings for cutting crown molding flat on a compound miter saw from the wall corner angle and the molding's spring angle: miter = atan(sin(spring) / tan(corner/2)) and bevel = asin(cos(spring) × cos(corner/2)), plus the miter setting for cutting the molding nested (upside-down against the fence) and which end of each piece to keep.

**Use when:** You need miter and bevel settings for inside or outside crown molding corners, including non-square corners such as 135° bay-window walls.

**Do not use when:** The trim is flat stock such as baseboard or casing, where the miter is simply half the corner angle (45° for a square corner; use baseboard-trim for quantities), or you need general angle trigonometry (use trigonometry).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `corner_angle_degrees` | number | ° | optional, default 90 | Angle between the two walls measured inside the room with an angle finder: 90 for a square corner, 135 for a typical bay-window corner. Drywall corners are rarely exactly 90°. (min 60, max 180) |
| `spring_angle_degrees` | number | ° | optional, default 38 | Angle between the back of the molding and the wall when installed: 38 for the common 52/38 profile, 45 for 45/45 crown, 52 for 38/52 crown (the number printed on the profile is sometimes the ceiling angle, so check with a square). (min 0, max 90) |
| `corner_type` | enum: inside \| outside |  | optional, default "inside" | Inside (concave) or outside (convex) corner; the angles are identical, only the fence side and the end to keep differ. |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `miter_angle_degrees` | number | ° | Saw-table (miter) setting for the molding lying flat: atan(sin(spring) / tan(corner/2)). |
| `bevel_angle_degrees` | number | ° | Blade-tilt (bevel) setting for the molding lying flat: asin(cos(spring) × cos(corner/2)). |
| `nested_cut_angle_degrees` | number | ° | Miter setting with the bevel at 0° when the molding is cut upside-down and nested against the fence at its spring angle: 90° − corner/2. |
| `ceiling_angle_degrees` | number | ° | 90° − spring angle: the angle between the molding and the ceiling. |
| `cutting_instructions` | string |  | Fence side, miter direction and which side of the blade to keep for the left and right pieces (left-tilting single-bevel saw). |

## Formula

`miter = atan(sin(spring_angle) / tan(corner_angle/2)); bevel = asin(cos(spring_angle) × cos(corner_angle/2)); nested miter = 90° − corner_angle/2 (bevel 0°); ceiling angle = 90° − spring_angle.`

Standard compound-miter formulas for a molding lying flat on the saw table; for a 90° corner and a 38° spring angle they give the familiar 31.62° miter and 33.86° bevel, and 35.26° / 30.00° for 45° crown. The corner-piece instructions follow the usual saw-manual chart for a left-tilting saw; cut and test a short offcut pair before cutting to length.

## Data Sources

- Wikipedia – Crown molding — https://en.wikipedia.org/wiki/Crown_molding (reference, retrieved 2026-09-24)
- Wikipedia – Miter saw (compound miter saws) — https://en.wikipedia.org/wiki/Miter_saw (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/crown-molding-miter?`
- `POST https://tttkmbb.com/api/v1/calculate/crown-molding-miter` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/crown-molding-miter · OpenAPI operationId `calculate_crown_molding_angles` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "crown-molding-miter", "inputs": {…}}`

## Example

- 90° inside corner, 52/38 crown (38° spring): inputs `{"corner_angle_degrees":90,"spring_angle_degrees":38,"corner_type":"inside"}` → `{"miter_angle_degrees":31.62,"bevel_angle_degrees":33.86,"nested_cut_angle_degrees":45,"ceiling_angle_degrees":52}`
- 135° outside corner (bay window), 45° crown: inputs `{"corner_angle_degrees":135,"spring_angle_degrees":45,"corner_type":"outside"}` → `{"miter_angle_degrees":16.32,"bevel_angle_degrees":15.7,"nested_cut_angle_degrees":22.5}`

```
GET https://tttkmbb.com/api/v1/calculate/crown-molding-miter?corner_angle_degrees=90&spring_angle_degrees=38&corner_type=inside
```

## Limitations

The trim is flat stock such as baseboard or casing, where the miter is simply half the corner angle (45° for a square corner; use baseboard-trim for quantities), or you need general angle trigonometry (use trigonometry). Standard compound-miter formulas for a molding lying flat on the saw table; for a 90° corner and a 38° spring angle they give the familiar 31.62° miter and 33.86° bevel, and 35.26° / 30.00° for 45° crown. The corner-piece instructions follow the usual saw-manual chart for a left-tilting saw; cut and test a short offcut pair before cutting to length. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Which is the spring angle on 52/38 crown?**

The angle between the molding's back and the wall, 38° for the common 52/38 profile (52° is the angle to the ceiling). Hold the piece against a framing square: the wall-side angle is the spring angle.

**Flat or nested: which method should I use?**

Nested (upside-down, at the spring angle against the fence) needs only a miter setting of 90° − corner/2 but requires the molding to fit under the fence; wide crown is cut flat with the compound settings given here.

**My saw tilts right, not left.**

Swap left and right in the instructions (mirror the fence side and the piece to keep); the miter and bevel values are unchanged.

## Related

- [Baseboard Trim Calculator](https://tttkmbb.com/construction/baseboard-trim.md) — Quantity of baseboard or flat trim for the same room.
- [Trigonometry Calculator](https://tttkmbb.com/math/trigonometry.md) — Evaluate the sine, cosine and tangent used by the formulas.
- [Angle Converter](https://tttkmbb.com/conversion/angle.md) — Convert between degrees and radians.