The Fillet Weld Size Calculator helps welders, structural engineers, and fabrication inspectors find the right size of a fillet weld to safely join metal parts. Correct weld sizing is critical for strength, safety, and code compliance. Using this calculator, you can check leg size, throat thickness, and ensure the weld can carry the required load without wasting filler material or risking failure. This tool is part of the Welding Design and Structural Connection Calculator category and is widely used in construction, shipbuilding, and mechanical fabrication.
formula of Fillet Weld Size Calculator
- Fillet Weld Leg Size (s):
This is the length of each leg of the right-angle triangle forming the fillet weld. - Throat Thickness (t):
The throat is the shortest distance from the weld root to the hypotenuse (fusion face).
Throat (t) = 0.707 × s
Where:
s = leg length of the fillet weld (mm or inches)
0.707 is sin(45°) for a right-angle triangle. - Required Leg Size for a Given Load:
First, find the required throat area:
Required Throat Area = F / Allowable Stress
Then,
t = Required Throat Area / Weld Length
Finally,
s = t / 0.707 - Fillet Weld Strength:
For static loading:
Fillet Weld Strength = Allowable Stress × Effective Throat × Weld Length
This checks if the weld can handle the design force safely.
Common Fillet Weld Sizes and Strengths Reference Table
This table shows typical fillet weld sizes with their throat thickness for quick checks.
| Leg Size (s) (mm) | Throat Thickness (t) (mm) | Note |
|---|---|---|
| 6 | 4.24 | Common in light structures |
| 8 | 5.66 | Standard for medium loads |
| 10 | 7.07 | Used in heavy frames |
| 12 | 8.49 | Heavy-duty connections |
| 16 | 11.31 | Structural steelwork joints |
This helps verify your calculated weld size against standard practice.
Example of Fillet Weld Size Calculator
Let’s work through a clear example.
A fillet weld must resist a force of 10,000 N.
Allowable Stress for the weld metal is 150 N/mm².
Weld Length is 100 mm.
- Required Throat Area:
A = F / Allowable Stress = 10,000 / 150 = 66.67 mm² - Throat Thickness:
t = A / Weld Length = 66.67 / 100 = 0.667 mm - Leg Size:
s = t / 0.707 = 0.667 / 0.707 ≈ 0.94 mm
This shows the required leg size is about 0.94 mm, but in practice, welders use standard minimum sizes—typically no smaller than 3 mm. So, you would choose a practical leg size above this minimum for safety and code compliance.
Most Common FAQs
The throat is where the actual stress passes through the weld. It directly determines how strong the weld is under load. A weak throat can cause cracking or failure.
No. Guessing can waste material or worse, cause unsafe joints. Always calculate using the load, material strength, and design codes.
Use the calculator to find leg and throat sizes. Then confirm with your project’s welding standards (like AWS D1.1 or Eurocode). Always follow inspection procedures to verify weld quality.