Fillet Weld Size Calculator
Throat and leg size a fillet weld needs for a load, and the capacity of a weld you already have.
Results
Weld throat
3.000
mm
Weld leg
4.243
mm
Force
70.711
kN
Stress
84.853
MPa
Utilisation
84.85
%
What this tool does
A fillet weld is checked on its throat — the shortest distance through the triangle — and for the usual equal-leg weld that is the leg times 0.707. Doubling the leg therefore doubles the strength but roughly quadruples the deposited metal and the distortion, which is why long thin welds beat short fat ones. The allowable stress depends on the electrode, the steel grade and the code, so take it from the specification rather than the default.
Formula
a = F ÷ (L × τ) ; z = a ÷ 0,707
Variables
| Symbol | Meaning | Unit |
|---|---|---|
fo | Force | kN |
lw | Weld length | mm |
ta | Allowable stress | MPa |
zz | Weld leg | mm |
AR | Weld throat | mm |
ZR | Weld leg | mm |
CA | Force | kN |
SA | Stress | MPa |
UT | Utilisation | % |
Worked example
- Force60 kN
- Weld length200 mm
- Allowable stress100 MPa
- Weld leg5 mm
- Weld throat3.000 mm
- Weld leg4.243 mm
- Force70.711 kN
- Stress84.853 MPa
- Utilisation84.85 %
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.