How it works
The legs stand on edge on the base, so from the front you see the board thickness. The long leg runs to the tip and the short leg leans against it.
The long leg's outer edge is the leg rise above the base divided by the cosine of the angle. The short leg is shorter by the board thickness divided by the sine of twice the angle.
The foot of both legs is cut at the leg angle (e.g. 20°), the top at 90° minus twice the angle (e.g. 50°) — both off square, as on a mitre saw scale.
The base equals the spread of the legs plus the overhang on each side. All pieces then go into a cut list with the saw kerf.
What the calculator assumes
- Height runs from the underside of the base to the tip, without the feet; the feet lie flat under the base.
- Leg lengths are on the longer, outer edge. The calculator does not cover joints, screws or stability — fix a tall tree to the wall.
Questions
- What angle do I cut the legs at?
- With legs 20° off vertical, cut the foot of both legs at 20° and the top at 50°. The tip angle is 40°.
- Why are the legs different lengths?
- The long leg runs to the tip and the short one leans against it, so it ends a little lower. With 20 mm boards and a 20° angle the difference is 31 mm.
Planning aid only. It does not size structural members or check loads — follow the manufacturer's instructions and your local building rules.