Calculator
Example data table
| Case | Leg a | Total length | Lines | Stress basis | Capacity |
|---|---|---|---|---|---|
| A | 6 mm | 300 mm | 2 | 120 MPa | ~305 kN |
| B | 1/4 in | 12 in | 2 | 18 ksi | ~76 kip |
| C | 8 mm | Rectangle 120×80 mm | 1 | ASD from FEXX | Varies by FEXX |
Example values are illustrative; confirm with your governing code and project requirements.
Formula used
- t = a · sin(θ) (effective throat)
- A = t · L_total · n (effective weld area)
- Capacity = A · τ (shear capacity using chosen stress basis)
For a typical 45° fillet, sin(45°) ≈ 0.707, so t ≈ 0.707a. If you select an FEXX-based method, the calculator converts FEXX to an equivalent shear stress using the chosen approximation.
How to use this calculator
- Select the unit system that matches your drawings.
- Enter leg size, angle, and number of weld lines.
- Choose how total length is defined (direct, rectangle, circle).
- If intermittent, enter segment length and segment count.
- Select a method: custom stress or FEXX-based approximation.
- Optionally enter an applied load to see utilization.
- Press Submit to view results above the form.
- Use the export buttons to download CSV or PDF.
Professional field guide for fillet weld sizing
1) What the calculator is solving
Fillet welds transfer load through a triangular throat, not the leg you measure with a gauge. This calculator converts leg size, weld angle, and welded length into effective throat and area, then estimates shear capacity using your selected stress basis. It supports quick comparisons during detailing, estimating, and shop planning.
2) Effective throat and why angle matters
For common equal-leg welds, the 45° geometry produces a throat near 0.707a. In the field, fit-up, bevels, or unequal legs can shift the included angle, reducing or increasing the effective throat. Using t = a·sin(θ) keeps geometry transparent and documents assumptions for reviewers and inspectors.
3) Total length, segments, and real coverage
Capacity is proportional to welded length, so length definition is critical. Continuous welds use the full length or a perimeter. Intermittent welds use segment length and count to model effective fused length. This supports stitch layouts on stiffeners, clips, and light framing where continuous welding is unnecessary.
4) Selecting a stress basis responsibly
Projects often specify allowable stress, resistance factors, or electrode strength. The calculator offers a custom allowable input for direct control, plus common FEXX-based approximations for fast comparisons. Use governing specifications, connection type, and loading conditions to choose the basis; the tool is intended for preliminary checks and clear reporting.
5) Unit control and consistent reporting
Mixing units is a frequent source of errors on site. Metric mode expects millimeters, MPa, and kN, while imperial mode expects inches, ksi, and kip. Confirm that electrode strength and allowable stress match the chosen system. Exports capture inputs and results so the same numbers can be reviewed later without re-entry.
6) Utilization checks for quick decisions
When an applied load is provided, the calculator reports utilization and a simple pass or fail indicator. Utilization near 1.0 signals limited reserve, which may require longer welds, more lines, higher strength consumables, or revised load paths. Eccentricity, fatigue, and discontinuities may require additional analysis.
7) Quality considerations beyond math
Weld size is only one factor in connection performance. Surface preparation, joint access, electrode storage, travel speed, and interpass temperature influence soundness. Field verification should include visual inspection, proper leg measurement, and—when specified—NDT. Recording design inputs alongside inspection results strengthens traceability for audits and handover packages.
8) Using exports for submittals and coordination
Clear records reduce RFIs and rework. After you calculate capacity, download the CSV for spreadsheets or the PDF for sharing with supervisors, engineers, and inspectors. Include the weld pattern, length definition, and selected method in submittal notes. Consistent reporting aligns shop drawings, installation, and final acceptance. Attach the PDF to inspection reports and keep the CSV in your project folder for future revisions and pricing change orders.
FAQs
1) What is a fillet weld throat?
The throat is the shortest distance from the weld root to the weld face. It governs effective area and strength, not the measured leg size alone.
2) Why does the calculator ask for weld angle?
Angle changes the effective throat through t = a·sin(θ). A smaller angle reduces throat and capacity for the same leg measurement.
3) When should I use intermittent weld mode?
Use it for stitch welds where only segments are welded. Enter segment length and count to represent total fused length used in capacity.
4) What does FEXX represent?
FEXX is the electrode tensile strength classification used for weld metal. The calculator can estimate shear capacity from FEXX using common approximations for quick checks.
5) Why do my results change between unit systems?
Metric uses mm, MPa, and kN, while imperial uses in, ksi, and kip. Ensure every input follows the selected unit system to avoid accidental scaling errors.
6) What does utilization mean?
Utilization is applied load divided by capacity. Values at or below 1.0 indicate the weld capacity meets the applied load under the chosen assumptions.
7) Does this replace engineering review?
No. It supports estimating and transparent documentation. Final design should consider eccentricity, fatigue, base-metal limits, detailing rules, and project specifications.
Measure wisely, weld safely, and document every verified result.