Infill Strength Calculator
Estimates a relative strength score for a 3D-printed part based on infill percentage, wall thickness, and top/bottom layers. Use it when optimizing slicer settings for structural versus lightweight parts.
About this calculator
A printed part's mechanical strength comes from three main contributors: internal infill, perimeter walls, and top/bottom solid layers. This calculator produces a composite strength index using the formula: Strength Score = (infill_percentage × 0.4) + (wall_thickness × 15) + (top_bottom_layers × 8). The coefficients reflect the relative contribution of each factor — walls carry the most load per unit input, which is why experienced makers often prefer more wall perimeters over high infill for structural parts. Infill contributes broadly but with diminishing returns above 40–50%. Top and bottom layers prevent surface delamination and improve compression resistance. The resulting score is a relative index, not a Pascal value, but it lets you compare configurations quickly. For most functional parts, a score above 80 indicates robust construction.
How to use
Suppose you are printing a functional bracket with 25% infill, 1.6 mm wall thickness, and 4 top/bottom layers. Apply the formula: Strength Score = (25 × 0.4) + (1.6 × 15) + (4 × 8) = 10 + 24 + 32 = 66. Now increase walls to 2.4 mm and keep everything else the same: Score = 10 + (2.4 × 15) + 32 = 10 + 36 + 32 = 78. This shows that adding wall thickness improved the score by 12 points — more efficiently than raising infill from 25% to 55% (which would only add 12 points as well, at the cost of much more material and time).
Frequently asked questions
Is it better to increase infill percentage or wall thickness for a stronger 3D print?
For most structural applications, increasing wall thickness (perimeter count) delivers more strength per gram of material than raising infill. Walls are printed in continuous extrusion paths that bond well and resist both tension and bending. Infill, by contrast, is a sparse internal lattice that primarily resists compression and supports top surfaces. Research and practical testing consistently show that going from 2 to 4 perimeters increases tensile strength more than going from 20% to 50% infill. A good rule of thumb is to max out walls first, then add infill only if compression resistance is critical.
What infill percentage should I use for functional 3D-printed parts?
For decorative or non-load-bearing prints, 10–15% infill is sufficient to support top surfaces. Functional parts that experience moderate stress — brackets, enclosures, jigs — typically perform well at 20–30% infill combined with 3–4 perimeter walls. Parts under high stress or impact loading benefit from 40–60% infill, but beyond 60% the strength gains diminish while print time and material cost rise sharply. For maximum strength, consider 100% infill or switching to a denser pattern like gyroid or cubic instead of pushing percentage higher.
How do top and bottom layers affect the strength and quality of a 3D print?
Top and bottom solid layers create a fully closed surface that protects infill from delamination and external loads. Too few layers (1–2) will cause the top surface to sag into sparse infill, creating a pillowing effect and weak surface finish. Three to four layers is the standard minimum for a clean, strong surface at typical layer heights. For parts under compression from above — like feet or platforms — increasing to 5–6 layers noticeably improves load distribution. Bottom layers also influence bed adhesion; more solid layers spread stress across a larger interface, reducing the chance of warping or layer separation.