Calculator inputs
The page uses a single-column flow, while the inputs follow a responsive three, two, and one column grid.
Formula used
1. Throat factor: k = sin(included angle / 2)
2. Effective throat: t = leg size × k
3. Effective area: A = t × effective weld length × number of weld lines
4. Design stress: fd = (base stress × efficiency) / safety factor
5. Required leg size: legreq = load / (fd × length × lines × k)
This calculator sizes fillet welds for direct shear demand using effective throat area. It does not replace project specifications, code checks, eccentric weld group analysis, fatigue review, or qualified engineering judgment.
Use it for early sizing, comparison studies, takeoff support, and fast field verification when the loading path is straightforward.
How to use this calculator
- Enter the factored or governing design load in kilonewtons.
- Add the usable weld length for one line and choose how many weld lines share the load.
- Set the included angle. For standard equal-leg fillet welds, use 90 degrees.
- Choose a stress input method. Either derive a base stress from electrode strength or type a direct allowable stress.
- Apply efficiency, safety factor, and any length deduction you need.
- Optionally enter a provided weld leg size to check capacity and utilization.
- Press Calculate weld size. The result appears above the form, followed by the graph and export buttons.
Example data table
| Design load (kN) | Length per line (mm) | Lines | Angle (°) | Design stress (MPa) | Required leg (mm) | Recommended leg (mm) |
|---|---|---|---|---|---|---|
| 120 | 180 | 2 | 90 | 98.00 | 4.81 | 5.0 |
| 185 | 220 | 2 | 90 | 110.00 | 5.41 | 6.0 |
| 260 | 250 | 4 | 100 | 95.00 | 4.62 | 5.0 |
Frequently asked questions
1. What does this weld size calculator estimate?
It estimates the required fillet weld leg size for direct shear loading. It also checks a provided weld size, reports throat area, evaluates utilization, and gives a rounded practical recommendation.
2. Why is effective throat important?
Effective throat is the resisting depth of the fillet weld. Capacity depends on that throat multiplied by effective length and weld lines, not only on the visible leg dimension.
3. Can I use this for groove welds?
Not directly. This page is arranged for fillet weld sizing under direct shear. Groove weld design can involve different effective area rules, joint preparation, and strength limits.
4. What is the difference between required and recommended size?
Required size comes from the math. Recommended size compares that value with a practical minimum based on connected thickness, then rounds upward to a field-friendly increment.
5. Why would I deduct weld length?
Length deductions can reflect end conditions, incomplete effective length, start-stop zones, or details where the full geometric length should not be counted as resisting weld.
6. Should I use factored load or service load?
Use the load format that matches your chosen stress basis and design method. Keep the load, allowable stress, resistance assumptions, and safety factors consistent throughout the calculation.
7. Does the chart replace a detailed weld group analysis?
No. The chart is a quick comparison tool. Eccentric loading, combined stresses, fatigue, dynamic effects, and code-specific checks still need separate engineering review.
8. Can I export the results?
Yes. After calculation, use the CSV button for spreadsheet-friendly output or the PDF button for a portable summary you can share or store.