Christmas tree· 4 min read
How to Make a Wooden Christmas Tree from Boards: Lengths and Cut Angles
A wooden A-frame Christmas tree from 100 × 20 mm boards: how to get the exact leg and base lengths from the angle, which mitre angles to cut and what to buy.
An A-frame wooden Christmas tree takes five pieces of board: two legs, a base and two feet. Hang fairy lights and baubles on it and take it apart after the holidays. The whole trick is in the angles — get them right and the legs meet cleanly at the tip and the tree stands straight. Here is how to work them out.
How the tree goes together
- Two legs of 100 × 20 mm board (about 4 × ¾ in) stand on edge on the base — 20 mm shows at the front and the frame is 100 mm deep.
- The long leg runs to the tip. The short leg leans against the inner edge of the long one at the top.
- The base lies flat and the legs are screwed into it from below.
- Two feet lie across under the base and stop the tree tipping forwards or backwards.
Angles: everything comes from the leg slope
Choose how far the legs lean from vertical. 20° makes a slim tree, 25° a wider one. Every cut follows from that one angle:
- Foot of both legs: cut at the slope angle — 20° for a 20° slope. The leg then sits flat on the base.
- Top of both legs: 90° minus twice the slope — 50° for a 20° slope. Cut like this, the short leg sits flush against the long one.
- Tip angle is twice the slope — 40° for a 20° slope.
The angles are off square, exactly as you set them on a mitre saw scale. Both cuts on a leg slant towards its inner edge, so the outer edge is the longest — measure the length along it.
How the lengths are worked out
- 1Leg rise above the base = frame height minus the base thickness. For a 1,800 mm frame and 20 mm board that is 1,780 mm.
- 2Long leg = leg rise ÷ cos(slope). At 20°: 1,780 ÷ 0.9397 = 1,894 mm.
- 3Short leg is shorter by the board thickness ÷ sin(2 × slope), i.e. 20 ÷ 0.6428 = 31 mm: 1,863 mm.
- 4Base = 2 × leg rise × tan(slope) = 2 × 1,780 × 0.364 = 1,296 mm — exactly under the feet of the legs. If you want the base to stick out, add the overhang on each side.
Two trees: large and small
| Tree | Long leg | Short leg | Base | Feet |
|---|---|---|---|---|
| Large, 1,800 mm frame, 20° | 1,894 mm | 1,863 mm | 1,296 mm | 2 × 500 mm |
| Small, 1,000 mm frame, 20° | 1,043 mm | 1,012 mm | 713 mm | 2 × 400 mm |
| Wider, 1,800 mm frame, 25° | 1,964 mm | 1,938 mm | 1,660 mm | 2 × 500 mm |
At a 25° slope the cuts become 25° at the foot and 40° at the top. The tree is 364 mm wider but the legs are only 70 mm longer. With 20 mm feet under the base, the large tree stands 1,820 mm tall and the small one 1,020 mm.
Christmas treeWork out a tree to your sizeHow many boards to buy
The example uses 4 m (about 13 ft) boards, a 3 mm saw kerf and a 5 mm squaring cut at the start of each board. Enter your own board lengths in the calculator — in the US, for example, 8 or 10 ft 1×4s.
- Large tree — 2 boards: both legs from the first (232 mm left), the base and both feet from the second (1,690 mm left).
- Small tree — 1 board: legs, base and feet with 412 mm left.
- Both at once — 3 boards, with almost 2 m left on the last one for another project.
Step by step
- 1Cut the foot of the long leg at 20°. Measure the length along the outer edge from it and cut the top at 50°, slanting towards the inner edge. Repeat for the short leg.
- 2Lay the legs together on a flat floor: the top of the short leg rests against the inner edge of the long one. Check that both feet are on one straight line.
- 3Join the tip — for example with two 8 mm wooden dowels and wood glue. Drill through both legs at once so the holes line up.
- 4Lay the feet parallel and the base across them; screw them together from below.
- 5Stand the A-frame on the base and screw the legs on from below through the base into their feet. Drill pilot holes so the wood does not split.
- 6Sand the edges. Untreated spruce greys indoors over time, so you may want to finish it with an interior wood stain.
Use fairy lights according to the maker's instructions and only ones rated for indoor use. With small children or pets at home, fix a tall tree to the wall.