Kerf Bend Calculator
Calculate the exact number of kerf cuts, spacing, bend allowance, and flat pattern length for precise wood and sheet material bending.
Input Parameters
Ratio of neutral axis position to thickness. Select a material preset for typical values.
Fill in all required fields to see results
How to Use & Formulas
- Select your unit system — inches (US standard) or millimeters.
- Choose a material preset or enter a custom K-factor.
- Enter material thickness — the full thickness of your stock.
- Enter bend radius — the desired inside (or outside) radius of the curve.
- Enter bend angle — the total angle you want the material to bend (e.g., 90° for a right angle).
- Enter kerf width — the width of each saw cut (blade kerf). Typical table saw blades are 1/8″ (0.125″).
- Results update automatically as you type. Use the diagram to visualize the cut pattern.
Bend Allowance (BA)
BA = (π / 180) × Angle × (Radius + K × Thickness)
The arc length of the neutral axis through the bend zone.
Outside Setback (OSSB)
OSSB = (Radius + Thickness) × tan(Angle / 2)
Bend Deduction (BD)
BD = 2 × OSSB − BA
Amount to subtract from total outside dimensions to get flat length.
Number of Kerf Cuts
N = ⌈(π / 180 × Angle × Radius) / Kerf Width⌉
The total cuts needed, rounded up, to achieve the bend without cracking.
Kerf Spacing
Spacing = Arc Length / Number of Cuts
Center-to-center distance between each kerf cut along the outer surface.
- Cut kerf slots approximately 85–90% through the material thickness — never cut all the way through.
- Always test on scrap material first to verify the bend radius and kerf spacing before cutting your workpiece.
- Use a backer board when cutting kerfs on a table saw to prevent tear-out.
- Apply wood glue into the kerfs before bending for a stronger finished curve.
- For tighter radii, use thinner kerf cuts and closer spacing.
- Clamp the piece to a form or jig matching your desired radius while the glue dries.
- Grain direction matters — cuts perpendicular to the grain work best for wood bending.
The K-factor represents the position of the neutral axis within the material thickness during bending:
- K = 0: Neutral axis at the inside surface (maximum compression)
- K = 0.5: Neutral axis at the center of the material
- K = 0.33: Common default for most materials and air bending
Typical K-factor values vary by material and bending method. Select a material preset for standard values, or measure from test bends for precision work.
