FDM Extrusion Width & Wall Planner
FDM / FFFIn FDM/FFF, the actual deposited bead width is not equal to the nozzle diameter — it depends on layer height, flow rate, and material viscosity. Knowing the true extrusion width lets you plan wall perimeter counts precisely, avoid under-extrusion gaps in thin walls, and ensure structural parts have at least two solid perimeters.
Machine presets
Most common FDM setup.
Inputs
Results
Simple model: 0.400 mm (D × k)
Structural wall
4 × 0.357 mm
negative = gap
Wall perimeter table
Standard wall thicknesses and how many perimeters fit at the current nozzle, layer height, and flow settings.
| Nominal (mm) | Perimeters | Actual (mm) | Δ (mm) | Status |
|---|---|---|---|---|
| 0.400 | 1 | 0.357 | -0.0429 | ⚠ |
| 0.800 | 2 | 0.714 | -0.0858 | ⚠ |
| 1.20 | 3 | 1.07 | -0.129 | ⚠ |
| 1.60◀ | 4 | 1.43 | -0.172 | ⚠ |
| 2.00 | 6 | 2.14 | +0.142 | ⚠ |
| 2.40 | 7 | 2.50 | +0.0996 | ⚠ |
| 3.20 | 9 | 3.21 | +0.0137 | ⚠ |
| 4.00 | 11 | 3.93 | -0.0721 | ⚠ |
Δ > 0 means perimeters slightly overlap (slicer may trim). Δ < 0 means a small gap that infill may need to cover.
Extrusion width model
w_e = D_nozzle × k_flow + (π/4 − 1) × h_layer
A_target = D_nozzle × h_layer × k_flow- D_nozzle
- Nozzle orifice diameter[mm]
- k_flow
- Flow rate multiplier[1.0 = 100%]
- h_layer
- Layer height[mm]
- A_target
- Target extrusion cross-section area[mm²]
Slic3r / PrusaSlicer extrusion-width model. The (π/4 − 1) ≈ −0.215 term accounts for the flattened elliptical cross-section of the deposited bead against the build plate or previous layer. For tall layers (h > 0.5D), the simple model w_e ≈ D × k_flow is sufficiently accurate.
Wall planning rules
Minimum wall
≥ 0.8 × nozzle diameter. Below this, the slicer may skip the perimeter or produce under-extruded walls.
Structural minimum
≥ 2 perimeters (2× extrusion width). Single-perimeter walls have low inter-layer bond strength and are prone to splitting.
Perimeter match
Design wall = n × w_e avoids gap/overlap artefacts. Small mismatches (< ±5%) are absorbed by the slicer.
Layer height
25–75% of nozzle diameter maximises layer adhesion and print reliability.
Sources
- [1]Slic3r manual — Extrusion width — github.com/slic3r/Slic3r — wiki / Extrusion-Width
- [2]Griffiths, C.A. et al. (2016) — The effect of print speed and line width on FFF dimensional accuracy — J. Manuf. Process. 22, 2016
- [3]Turner, B.N. et al. (2014) — A review of melt extrusion additive manufacturing processes: I. Process design and modeling — Rapid Prototyping J. 20(3):192–204
- [4]DfAM Checklist — additive.tools FDM design rules