Miter-Angle—Frame & Trim Cuts
Miter angle = half the corner angle. 90° corner: 45° each side. Polygon: miter = (180° − interior) ÷ 2. Set saw to miter (not bevel); account for kerf in layout.
Why This Construction Metric Matters
Why: Correct miter angles ensure tight joints in frames, trim, and crown molding. Wrong angles cause gaps and visible seams.
How: For 90°: miter = 45°. For polygon: interior = 180(n−2)/n; miter = (180−interior)/2. Set miter gauge, not bevel. Kerf compensation adjusts cut length.
- ●90° corner: 45° miter each side; set saw to 45°, not 90°.
- ●Hexagon: interior 120°; miter 30°. Octagon: interior 135°; miter 22.5°.
- ●Kerf: add half blade width per cut for inside dimensions.
- ●Test cut on scrap; compound miters need both miter and bevel.
Miter Angle Calculator
Frames • Polygons • Kerf • Saw settings • Joint types
Quick Examples — Click to Load
Picture Frame 90°
Standard 8x10" picture frame
Hexagonal Planter Box
6-sided planter with 120° corners
Octagonal Mirror Frame
8-sided mirror frame with 135° corners
Non-90° Wall Corner Trim
135° wall corner trim piece
Pentagon Birdhouse
5-sided birdhouse with 108° corners
Custom Angle Frame
Custom 67.5° angle frame
Triangle Sign Frame
Equilateral triangle with 60° corners
Square Box
Standard square box with 90° corners
Enter the angle where the two pieces meet (0° to 180°)
Miter Joint
Angled cuts meeting at corner, most common for frames
Width of the saw blade cut (kerf)
📊 Results
Miter Angle
45.00°
Saw Blade Setting
45.00°
Set miter saw to this angle
Kerf Allowance
0.1250"
Blade width compensation
Joint Tolerance
±0.3°
Acceptable gap
🔍 Joint Visualization
Blue lines: Corner angle | Green dashed: Miter cut angle
Step-by-Step Calculation
=== Miter Angle Calculation === Calculation Mode: Custom Angle Joint Type: Miter Joint Custom Corner Angle: 90° === Miter Angle Calculation === Miter Angle = (180° - 90.00°) / 2 Miter Angle = 45.0000° === Saw Blade Setting === Saw Blade Angle = 90° - 45.0000° Saw Blade Angle = 45.0000° === Material & Kerf === Material Width: 2 inches Kerf Width: 0.1250" Kerf Allowance: 0.1250" === Joint Information === Joint Type: Miter Joint Typical Gap Tolerance: ±0.25° Difficulty: Medium === Recommendations === Set your miter saw to: 45.00° Cut angle: 45.00° ⚠️ Wide kerf detected - consider adjusting for kerf compensation Joint difficulty: Medium - Picture frames, trim, moldings
📈 Visualizations
📊 Common Angle Comparison
🔺 Polygon Interior Angles
Planning estimates only. Verify with a licensed engineer or contractor before construction.
📐 Construction Industry Facts
90° corner: miter = 45° each side; saw set to 45°.
— Woodworking
Polygon miter = (180° − interior) ÷ 2; interior = 180(n−2)/n.
— Geometry
Miter gauge for angle; bevel for compound cuts.
— Saw manual
Kerf compensation: add half blade width per cut.
— Best practice
📋 Key Takeaways
- • 90° corner: Miter = 45° each side
- • Polygon: Miter = (180° − Interior) / 2
- • Saw: Set to miter angle (not bevel)
- • Kerf: Account for blade width in layout
What is a Miter Angle Calculator?
A miter angle calculator helps you determine the precise cutting angle needed for miter joints in frames, trim, and polygon projects. When two pieces meet at a corner, each piece must be cut at half the supplement of the corner angle. This calculator handles both custom angles and polygon shapes, accounts for blade kerf (width), and provides saw blade settings for accurate cuts.
Precise Angles
Calculate exact miter angles for perfect joints
Polygon Support
Hexagons, octagons, and custom shapes
Kerf Compensation
Account for blade width in cuts
Saw Settings
Direct miter saw angle settings
How to Calculate Miter Angles
Basic Formula
For a 90° corner: (180° - 90°) / 2 = 45°
Polygon Formula
For hexagon (6 sides): (6-2) × 180° / 6 = 120°
Common Miter Angles
Common Applications
Picture Frames
Standard 90° corners
Planter Boxes
Hexagonal and octagonal
Mirror Frames
Octagonal frames
Wall Trim
Baseboards and crown molding
Box Construction
Square and custom boxes
Decorative Pieces
Triangle and pentagon shapes
Door Frames
Custom angle frames
Window Trim
Casing and molding
Joint Types Reference
| Joint Type | Difficulty | Gap Tolerance | Typical Use |
|---|---|---|---|
| 📐 Butt Joint | Easy | ±0.5° | Basic frames, simple boxes |
| 🔺 Miter Joint | Medium | ±0.25° | Picture frames, trim, moldings |
| 📏 Scarf Joint | Advanced | ±0.3° | Long boards, trim extensions |
| 🔗 Lap Joint | Medium | ±0.4° | Box construction, drawers |
Polygon Reference
Triangle
Uses: Small frames, Decorative pieces, Signs
Square
Uses: Picture frames, Boxes, Windows
Pentagon
Uses: Decorative frames, Pentagon boxes, Architectural elements
Hexagon
Uses: Planter boxes, Honeycomb patterns, Hexagon frames
Heptagon
Uses: Decorative pieces, Custom frames
Octagon
Uses: Mirror frames, Stop signs, Octagon boxes
Nonagon
Uses: Decorative elements, Custom projects
Decagon
Uses: Decorative frames, Custom designs
Kerf Compensation
Blade kerf removes material. For tight joints, add half-kerf to each cut or use a sled. Typical saw kerf: 0.08–0.12".
Key Formulas
Important Considerations
⚠️ Avoid
- • Cutting without testing first
- • Ignoring blade deflection
- • Wrong bevel for compound miters
✓ Best Practices
- • Cut test pieces first
- • Use sharp blade for clean miters
- • Account for kerf in layout
⚠️ Disclaimer: Miter angles are theoretical. Actual cuts may need adjustment for blade deflection, material thickness, and joint fit.
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