Overhang Angle & Support Calculator
Your real overhang threshold from line width and layer height — the 45 degree rule is a ratio rule wearing an angle for a label.
Your threshold at every layer height
Overlap remaining at each angle
The 45° rule is really "layer height = half the line width"
Each layer steps outward from the one below by layer height × tan(angle), and it holds if enough of the line still sits on the layer beneath. Take half the line as the threshold and the angle falls straight out of the settings: tan θ = width ÷ (2 × height). At the near-universal 0.42 mm line and 0.2 mm layer that's 46.4° — which rounds to 45, and is the entire reason the rule works.
So it's a ratio rule in an angle's clothing. At exactly layer = half line width the threshold is exactly 45.0°, and it stays exactly 45 for 0.42/0.21, for 0.63/0.315 and for 0.84/0.42 alike — the absolute sizes don't matter, only the ratio. The number 45 is a coincidence of where the common defaults happen to sit.
And it moves a long way when the layer height does. At 0.1 mm the threshold is 64.5° — eighteen degrees of overhang capability most people never use — and at 0.3 mm it's 35°, eleven degrees they're exceeding without knowing. Halving the layer height on an overhanging region is often cheaper than supporting it, and slicers that vary layer height by geometry are exploiting exactly this.
- Bridging obeys none of this. A bridge is stretched between two anchors and can run essentially horizontal, where the same angle unsupported would droop on the first layer. Bridges want speed and maximum cooling; overhangs want the opposite of speed. Turning an overhang into a bridge is usually the better redesign.
- Cooling decides more overhangs than angle does. A 55° overhang with strong part cooling often beats a 45° one without it. It's also why overhangs fail more in ABS — the material wants a warm chamber and the overhang wants a cold blast.
- The support material is the small cost. The marks left on the supported face are the real one, which is the argument for orienting the part so the supported surface is one nobody looks at.
- Orientation is a trade, not an optimisation. The orientation that minimises support very often puts the layer lines across the load — and a printed part is weakest between layers, so the easiest part to print is frequently the one that breaks.
How to use
- Enter the line width and layer height from your slicer profile.
- Read the real threshold for those settings rather than assuming 45 degrees.
- Try halving the layer height before adding support.
- Decide which surface must be good before deciding orientation.
Frequently asked questions
What is the 45 degree rule in 3D printing?
That an overhang steeper than 45 degrees from vertical needs support. It is real geometry with a misleading label: each layer steps outward from the one below by layer height times the tangent of the angle, and it holds while enough of the line still sits on the layer beneath. At 45 degrees with a 0.2 mm layer that step is 0.2 mm out of a 0.42 mm line, which leaves 52 per cent supported.
Is 45 degrees actually the right threshold?
For one particular pair of settings, yes. The threshold where half the line remains supported is tan(theta) = width divided by twice the height, which at the near-universal 0.42 mm line and 0.2 mm layer works out at 46.4 degrees. That rounds to 45 and is the whole reason the rule caught on — it is not a property of the process.
What does the 45 degree rule really depend on?
The ratio of layer height to line width, and nothing else. At exactly layer height equals half the line width the threshold is exactly 45.0 degrees, and it stays exactly 45 for a 0.42 mm line at 0.21, a 0.63 at 0.315 and an 0.84 at 0.42 alike. The absolute sizes do not matter; only the ratio does. It is a ratio rule in an angle costume.
Does layer height change the maximum overhang angle?
Enormously. On a 0.42 mm line, a 0.1 mm layer supports 64.5 degrees and a 0.3 mm layer only 35 — a spread of nearly thirty degrees from a setting most people change for surface finish alone. Anyone printing fine has eighteen degrees of overhang capability they are not using, and anyone printing coarse is exceeding the rule of thumb without knowing.
Can I avoid supports by printing at a finer layer height?
Very often, and it is worth trying before adding support. Halving the layer height moves the threshold up substantially — from 46 degrees to 64 in the common case — so a feature that needed support at 0.2 mm may print cleanly at 0.1. Slicers that vary layer height by geometry are exploiting exactly this, applying fine layers only where the overhang needs them.
Why can a bridge be horizontal when an overhang cannot?
Because it is a different mechanism. A bridge is stretched in tension between two anchored points, so it holds itself up while it cools; an unsupported overhang has nothing but the layer below to sit on. That is also why the two want opposite settings — a bridge wants speed and maximum cooling to freeze the strand, where an overhang wants slower movement so each pass sets before the next drags it.
Does cooling affect overhang quality?
It decides more overhangs than the angle does. The extrusion has to freeze before the next pass pulls on it, so a 55 degree overhang with strong part cooling often beats a 45 degree one without. It is also why overhangs are worse in ABS: the material wants a warm chamber to avoid warping and the overhang wants a cold blast, and you cannot have both at once.
How much support material will an overhang need?
Roughly the prism under the overhanging face at whatever density you set — but the material is the small cost. The real cost is the surface left behind, because support marks on a visible face are far harder to fix than the plastic is to buy. That is the argument for orienting a part so the supported surface is one nobody looks at.
How should I orient a part for printing?
Decide which surface must look good and which direction must be strong first, then accept whatever support that costs. Orientation is a trade rather than an optimisation — the orientation that minimises support very often puts the layer lines across the load, and a printed part is weakest between its layers, so the easiest part to print is frequently the one that breaks.
What angle is measured, from vertical or horizontal?
Conventionally from vertical, so a vertical wall is zero degrees and a flat ceiling is ninety. Slicers usually express the support threshold this way too, which means a setting of 45 supports anything more than 45 degrees away from vertical. Some communities quote it the other way round from horizontal, which is a common source of confusion when comparing settings.
Does line width affect overhangs?
It works in the opposite direction to layer height, and it is the lever people forget. A wider line has more material to hang over the step, so widening the line raises the threshold for the same layer height. Since line width is adjustable from about 100 to 150 per cent of the nozzle independently of everything else, it is a free way to buy a few degrees.
Why do my overhangs look rough even when they print?
Because an overhang is always a finish compromise, even a sound one. Each layer is partly hanging in air and sags slightly before it sets, so the surface is textured in a way a vertical wall is not. Clearing the geometric threshold means the part will build, not that the face will look like the ones beside it — if that surface matters, reorient rather than tune.
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