Infill Weight & Strength Calculator
Created by: Natalie Reed
Last updated:
See how different infill percentages affect your part weight, material cost, relative strength, and print time to choose the right infill for your application.
Infill Weight & Strength Calculator
3D PrintingCompare weight, cost, strength, and print time across different infill percentages for your part dimensions and material.
What is a Infill Weight & Strength Calculator?
An infill weight and strength calculator shows how different infill percentages affect the weight, material cost, relative strength, and print time of a 3D printed part. This is the question every 3D printer user asks: what infill should I use? The answer depends on what the part needs to do.
Infill is the internal structure printed inside the shell walls of a part. At 0% infill, the part is hollow. At 100%, it is completely solid. Most functional parts use 15-25% infill, which provides adequate strength for everyday use at a fraction of the weight and cost of a solid part. But the relationship between infill percentage and strength is not linear — doubling the infill does not double the strength.
This calculator takes your part dimensions, shell thickness, and material, then computes the weight, cost, and relative strength at five standard infill levels: 10%, 20%, 40%, 60%, and 100%. The strength values are based on empirical testing data showing that 20% infill already provides about 55% of the strength of a solid part, making it the sweet spot for most applications.
Understanding the weight-strength-cost relationship helps you avoid two common mistakes: using too little infill on functional parts that break in use, or using too much infill on parts where the extra weight, cost, and print time add no practical benefit.
How the Infill Weight & Strength Calculator Works
The calculator computes the bounding box volume, then subtracts shell walls and top/bottom solid layers to find the inner volume available for infill. Shell volume is approximated as the volume of the outer walls minus the inner cavity. The top and bottom solid volume comes from the layer height multiplied by the number of solid layers and the footprint area.
For each infill percentage, the infill volume is the inner volume multiplied by the percentage. Total weight combines shell, top/bottom, and infill volumes multiplied by material density. Cost uses the material price per kilogram. Relative strength values come from published empirical testing of PLA parts at each infill level.
Infill weight and strength formulas
Bounding box volume (cm³) = L × W × H / 1000
Top/bottom volume (cm³) = L × W × (layers × layer_height) / 1000
Shell volume (cm³) = (L×W×H - (L-2×shell)×(W-2×shell)×H) / 1000
Inner volume = bbox_volume - shell_volume - top_bottom_volume
Infill volume at X% = inner_volume × X / 100
Total weight (g) = (shell + top_bottom + infill_volume) × density
Relative strength from empirical data: 10%=40%, 20%=55%, 40%=70%, 60%=82%, 100%=100%
Example Calculations
Example 1: Small functional bracket
A 60×40×30mm bracket in PLA with 1.2mm shells and 4 top/bottom layers at 0.2mm. At 20% infill: approximately 32g weight, $0.64 material cost, 55% relative strength. At 40% infill: 39g, $0.78, 70% strength. The 7g weight increase adds 15% more strength — whether that matters depends on the loads involved.
Example 2: Decorative display piece
A 100×100×80mm decorative item in PETG. At 10% infill: approximately 120g, $2.64 cost, 40% strength. Since this is decorative, the 40% strength is more than enough and saves over $4 compared to 100% infill. The print also finishes about 40% faster at 10% vs 40% infill.
Example 3: Structural mounting plate
A 80×60×10mm flat mounting plate in ABS. At 60% infill: approximately 28g, $0.62 cost, 82% strength. For thin plates under bending stress, shell thickness matters more than infill. Four wall lines (1.6mm) plus 60% infill provides excellent rigidity for structural mounting applications.
Common 3D Printing Applications
- Choose the optimal infill percentage for functional parts by comparing the strength gain against the weight and cost increase.
- Minimize material usage on decorative and display prints where structural strength is not needed.
- Estimate total material cost for batch production at different infill levels to find the most cost-effective option.
- Compare PLA, PETG, and ABS weight and cost for the same part to inform material selection.
- Understand the diminishing returns of high infill percentages to avoid wasting material on parts that do not benefit.
- Plan print farm jobs by estimating total weight and spool consumption across multiple parts.
- Justify engineering decisions with data — show stakeholders the tradeoff between strength, weight, and cost.
Tips for Better 3D Printing Results
For most functional parts, start with 20% infill. It provides 55% of solid strength at roughly half the weight and cost. Only increase beyond 20% if your part will bear significant loads, contain threaded inserts, or undergo impact stress. Test a sample part at 20% before committing to higher infill for production runs.
Shell thickness often matters more than infill for bending resistance. If your part bends or flexes, try adding one or two more wall lines before increasing infill. This adds less weight and print time than increasing infill while often providing more improvement in the specific failure mode.
Frequently Asked Questions
What infill percentage should I use for functional parts?
For most functional parts, 20% infill provides a good balance of strength and material efficiency. Parts that need to bear significant loads or resist impact should use 40-60%. Only use 100% infill for parts under extreme stress — the weight and material cost increase dramatically with diminishing strength returns above 60%.
Does infill pattern matter for strength?
Yes, infill pattern affects both strength and print time. Gyroid is excellent for omnidirectional strength. Grid and triangles are strong in specific axes. Honeycomb provides good strength-to-weight ratio. Lightning infill uses the least material but only supports top surfaces — it offers almost no structural strength.
How much does infill affect print weight?
The weight increase depends on your part geometry, but as a general guide: going from 10% to 20% infill adds roughly 10-15% weight. Going from 20% to 100% can double or triple the weight. The shell walls and top/bottom layers add a fixed weight regardless of infill percentage.
Is 100% infill ever necessary?
Solid infill is needed for parts under extreme mechanical stress, threaded inserts that need maximum material around them, or parts that will be machined after printing. For most applications, 40-60% infill provides 70-82% of solid strength at a fraction of the weight, cost, and print time.
How does shell thickness affect strength more than infill?
For parts under bending stress, shell thickness has a larger impact than infill because the outer walls carry most of the load. Increasing from 2 to 4 wall lines can improve bending strength by 50% or more. Infill matters more for compression loads where the entire cross-section is under stress.
What is the cheapest infill percentage that still has some strength?
Ten percent infill is the minimum for parts that need any structural integrity. It provides about 40% of solid strength while using the least internal material. For purely decorative parts like vases or display models, you can go even lower or use vase mode with zero infill.
Does infill percentage affect print time significantly?
Yes, infill is one of the biggest factors in print time. Going from 10% to 100% infill can more than double the total print time. The increase is not linear — 20% infill might add 15% to print time compared to 10%, while 100% can add 130% or more. Infill at high percentages also increases flow rate demand.
Sources and References
- CNC Kitchen, comprehensive infill percentage vs tensile strength testing across multiple materials.
- Prusa Research, infill pattern comparison guide with strength and print time benchmarks.
- All3DP, infill percentage guide with recommendations by use case.
- Simplify3D, infill pattern properties and guidelines for functional printing.
- Filament Properties, material density and pricing data for PLA, PETG, and ABS filaments.