Calculation
amin = √tmax − 0.5; amax = 0.7 · tmin
Too-thin welds cool too fast and bond poorly; too-thick welds needlessly distort thin plates.
DIN EN 1993-1-8 (Richtwert)
Recommended fillet weld throat thickness range
Too-thin welds cool too fast and bond poorly; too-thick welds needlessly distort thin plates.
MINTSI
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Result
Select a target and calculate.
Understand the inputs
- Recommended minimum throat amin — Lower bound avoiding a mismatch between weld and part cross-section.
- Recommended maximum throat amax — Practical upper bound; not normatively fixed in DIN EN 1993-1-8.
- Largest plate thickness tmax — Thickness of the thicker of the two welded parts.
- Smallest plate thickness tmin — Thickness of the thinner of the two welded parts.
Example
tmax = 16 mm gives amin ≈ 3.5 mm; tmin = 10 mm gives amax = 7 mm.
Assumptions and limits
Experience-based guideline for flat products and open sections with t ≥ 3 mm; the effective throat should always be at least 3 mm.
Understand Recommended fillet weld throat thickness range
This calculator estimates the recommended lower and upper fillet weld throat thickness bounds from the largest and smallest plate thickness involved.
What does this quantity describe?
The lower bound amin = √tmax − 0.5 avoids a mismatch between the weld cross-section and the connected parts (too-thin welds cool too fast and bond poorly). The upper bound amax = 0.7·tmin is a practical guideline preventing an oversized weld from unnecessarily distorting the thinner plate through heat input.
Think of choosing the right nail size for two boards of different thickness: too thin a nail won't hold, too thick a nail splits the thinner board. The two formulas bracket the sensible range in between.
Formula and variables
amin = √tmax − 0.5; amax = 0.7 · tmin
amin = √tmax − 0.5 (mm)amax = 0.7 · tmin (mm)tmax = (amin + 0.5)²tmin = amax / 0.7
| Symbol / input | Meaning |
|---|---|
| Recommended minimum throat amin | Lower bound avoiding a mismatch between weld and part cross-section. |
| Recommended maximum throat amax | Practical upper bound; not normatively fixed in DIN EN 1993-1-8. |
| Largest plate thickness tmax | Thickness of the thicker of the two welded parts. |
| Smallest plate thickness tmin | Thickness of the thinner of the two welded parts. |
Choose the inputs correctly
tmax is the thickness of the thicker, tmin the thickness of the thinner of the two welded parts. Both formulas are defined only for values in millimetres.
How to use the calculator
Enter tmax to get amin, and tmin to get amax. The throat thickness actually chosen should fall between amin and amax and additionally be at least 3 mm.
Worked example
tmax = 16 mm gives amin = √16 − 0.5 = 3.5 mm; tmin = 10 mm gives amax = 0.7 · 10 = 7 mm.
Understand the result and units
A chosen throat thickness between 3.5 mm and 7 mm is considered constructively sound for this plate-thickness pair. Values outside this range are not automatically invalid but should be justified.
Both formulas are explicitly defined in millimetres (√tmax is not a dimensionally homogeneous operation); the results amin and amax are likewise given in mm.
Why the formula only works in millimetres
amin = √tmax − 0.5 is not a dimensionally homogeneous physical equation but an empirical rule of thumb calibrated exclusively for tmax in millimetres. Plugging in tmax in a different unit (e.g. inches or metres) gives a wrong numeric result, because the square-root function and the additive constant 0.5 do not scale along. This calculator therefore always computes internally in millimetres, regardless of the display unit chosen at the input field.
Typical applications
These rules of thumb are used in preliminary design to quickly suggest a sensible throat thickness for a given plate-thickness pair before a detailed strength calculation.
Assumptions, limits and common mistakes
The formulas apply to flat products and open sections with t ≥ 3 mm; the upper bound amax is not itself normatively fixed in DIN EN 1993-1-8 but a widely used practical guideline. For plate thicknesses of 30 mm or more, the code already accepts amin ≥ 5 mm.
Common mistake: A common mistake is treating amin or amax as mandatory code values rather than guidelines, or going below the 3 mm effective minimum throat even when the formula computes a smaller value.
Frequently asked questions
Is amin a code-mandated value?
It is a design rule to avoid a mismatch between weld and part cross-section, not a strength requirement; actual load-carrying capacity must be verified separately.
Why isn't the upper bound amax normatively fixed?
DIN EN 1993-1-8 gives no binding value here; 0.7·tmin has become an established practical rule to avoid excessive distortion.
What applies for very thick plates (t ≥ 30 mm)?
There, the code already accepts a minimum throat of 5 mm regardless of what the √tmax formula computes.
Can the throat be smaller than 3 mm?
No, the effective throat of a fillet weld should always be at least 3 mm, even if amin computes to a smaller value.
Does this calculator replace the strength check?
No, it only gives a constructive suggestion for throat thickness; actual capacity must be verified with the fillet weld shear stress and safety factor calculators.