Compound miter angles for a 4-sided planter with 15° sides
For a four-sided planter with sides tilted 15° from vertical, set the blade bevel to 43.1 degrees and the miter to 14.5 degrees, then rip the top and bottom edges at 15 degrees so the box sits flat and the rim is level.
How to work it out
- bevel = asin(cos 15° × sin(180° ÷ 4)) = 43.1°
- miter = atan(sin 15° × tan(180° ÷ 4)) = 14.5°
- Side board width = 12 in ÷ cos 15° = 12-7/16 in
- Top edge = 16 in + 2 × 12 in × tan 15° × tan(180° ÷ 4) = 22-7/16 in
A 15° flare is the classic tapered planter or bin: enough lean to read as tapered, not so much that the box looks unstable or tips when it is full of wet soil. The 43.1° bevel sits inside the tilt range of most compound miter saws, just short of the 45° stop.
Adjust for your project
- Table-saw miter gauge (reads 90° at square)
- 75.5 degrees
- Top & bottom edge bevel
- 15 degrees
- Side board width (up the slope)
- 12-7/16 in
- Bottom edge of each side (outside)
- 16 in
- Top edge of each side (outside)
- 22-7/16 in
- Angles are measured from square, the way most miter saws are marked: 0° miter and 0° bevel is a plain crosscut.
- Side boards are cut as trapezoids: the bottom edge is the base length and the top edge is longer, both measured on the outside face from long point to long point.
Planter with 15° sides, by number of sides
| Sides | Blade bevel (tilt) | Miter (table) angle | Table-saw miter gauge (reads 90° at square) |
|---|---|---|---|
| 3 | 56.8 degrees | 24.1 degrees | 65.9 degrees |
| 4 | 43.1 degrees | 14.5 degrees | 75.5 degrees |
| 5 | 34.6 degrees | 10.6 degrees | 79.4 degrees |
| 6 | 28.9 degrees | 8.5 degrees | 81.5 degrees |
| 8 | 21.7 degrees | 6.1 degrees | 83.9 degrees |
What to know about a planter with 15° sides
The side boards are wider than the planter is tall, because they lean. For a planter 12 in tall, each board is 12 ÷ cos 15° ≈ 12-7/16 in wide, measured up the slope. The top also grows: each side leans out about 3-1/4 in over that height, so the opening is roughly 6-7/16 in longer and wider than the base.
The common mistake at this angle is the rim. People cut the corner joints perfectly and then leave the top and bottom edges square, so the box rocks on its base and the top edge slopes outward. Rip both long edges of every side at 15° before cutting the corners — the bottom then sits flat on the ground and the top is level for a cap rail.
On a wide side board, a non-sliding miter saw may not reach through the cut at a 43.1° bevel. A table saw with the blade at 43.1° and the miter gauge at 75.5° (90° minus the miter) handles wide boards; cut one test corner in scrap and check it with a square before cutting the good stock.
Flip each board end for end between cuts so both ends lean the right way. Hold the bottom panel on cleats rather than trying to fit it to the sloped walls, and drill a few drainage holes.
Crown molding is this same geometry — its “sides” lean by the spring angle — which is why Crown molding miter angle for a 90° inside corner (38° crown) uses the same kind of bevel-plus-miter setting. For a flat, straight-sided six-piece version, see What miter angle for a hexagon.
Different size? Use the full Compound Miter Calculator.
What you’ll need
- Compound miter sawPremium price
Fast, repeatable crosscuts, miters and bevels for trim, frames and cut lists. A sliding model handles wider boards.
See options on Amazon (opens in a new tab) - Digital angle finderBudget price
Reads angles to a tenth of a degree — blade-to-fence, blade tilt and existing corners — so saw settings match the calculator.
See options on Amazon (opens in a new tab) - Band clamp with cornersBudget price
Pulls all the corners of a frame, hexagon or octagon together at once — the easiest way to glue a mitered ring.
See options on Amazon (opens in a new tab)
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Frequently asked questions
How wide should the side boards be for a 12 in tall planter with 15° sides?
About 12-7/16 in, measured up the slope: 12 in ÷ cos 15°. Buy stock a little wider and rip it to width after beveling the edges.
What bevel and miter for a 4-sided planter with 10° sides?
A blade bevel of 44.1 degrees and a miter of 9.9 degrees, with the top and bottom edges ripped at 10 degrees. A gentler flare, and the bevel is even closer to 45°.
What bevel and miter for a 6-sided planter with 15° sides?
A blade bevel of 28.9 degrees and a miter of 8.5 degrees. More sides mean smaller settings; the top and bottom edges are still ripped at 15 degrees.
What bevel and miter for an 8-sided planter with 15° sides?
A blade bevel of 21.7 degrees and a miter of 6.1 degrees. With sixteen corner cuts, test the settings on a full ring of scrap first.