Birdsmouth Cut Calculator

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Calculates the dimensions needed for a birdsmouth cut on a rafter, given the rafter's width and the desired depth and seat cut.

How To Use

How to use this calculator

Start with your values, or try a preset.

Step 1

Enter Rafter Width, Birdsmouth Depth, and Seat Cut Length in the units shown.

Step 2

Read Remaining Rafter Width After Cut and Heel Cut Length in the results panel. Results update as you change the inputs.

Step 3

Choose a preset to load an example, then adjust the values for your situation.

Worked Examples

See the inputs and their calculated results.

Rafter Width: 5.5 inches; Birdsmouth Depth: 1.5 inches; Seat Cut Length: 4 inches

Remaining Rafter Width After Cut: 4 inches; Heel Cut Length: 4.272001873 inches

Rafter Width: 5.5 inches; Birdsmouth Depth: 1 inches; Seat Cut Length: 3 inches

Remaining Rafter Width After Cut: 4.5 inches; Heel Cut Length: 3.16227766 inches

Rafter Width: 7.25 inches; Birdsmouth Depth: 2 inches; Seat Cut Length: 6 inches

Remaining Rafter Width After Cut: 5.25 inches; Heel Cut Length: 6.32455532 inches

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