Weld Design Calculator — Fillet & Butt Weld Strength, Fatigue Life & Heat Input (EN 1993-1-8)

Weld strength follows EN 1993-1-8:2005 §4.5.3.2 — Eurocode 3's directional method — throughout, with the recommended partial factor γ_M2 = 1.25. AWS D1.1 is used for one thing only: the prequalified minimum fillet weld sizes. It is NOT offered as an alternative strength method, because AWS D1.1 sizes welds from the electrode classification strength with its own resistance factor, which is a different model and not simply a different partial factor. Fatigue uses EN 1993-1-9:2005 §7.1/§8 with the γ_Mf partial factor. Quality acceptance follows ISO 5817. Heat input and t8/5 cooling time follow EN 1011-1 / EN 1011-2 Annex D. The governing clause and the check that actually governs are both shown in the generated PDF report.

The calculator handles direct shear/axial, in-plane bending, torsion (eccentric load) and combined loading (F + M + T) for both fillet welds and full- or partial-penetration butt welds. A separate eccentric-load panel covers rectangular weld groups under combined direct shear and torsion, resolving the shear vector at all four corners of the group.

Enter the detail category Δσ_C for your joint — read it from EN 1993-1-9 Tables 8.1–8.10, because the same physical weld falls in different categories depending on the detail, the direction of stress and the inspection level, and this tool does not classify geometry for you. Then enter the applied nominal stress range Δσ, the number of applied cycles, and the γ_Mf partial factor for your assessment method. The tool returns the endurance N_f from the two-slope design curve and the Miner damage ratio D = n / N_f; D < 1.0 is required. A range below the constant-amplitude limit is reported as formally infinite life but flagged as a caution, never as a clean pass.

ISO 5817 defines acceptance levels B (stringent), C (standard) and D (moderate) for weld imperfections — undercut, porosity, cracks, overlap, throat deviation and root concavity. The tool presents the limit table for your selected quality level so you can cross-check your weld inspection results against the standard.

Almost all of them. The weld strength check is EN 1993-1-8, the fatigue check is EN 1993-1-9, the quality limits are ISO 5817, and the heat input and t8/5 cooling time are EN 1011-1 and EN 1011-2 Annex D. One number is NOT: the preheat temperature shown beside the heat input. That is a MechanixCalc screening estimate keyed on carbon equivalent alone — it takes no plate thickness and no hydrogen level, both of which are first-order in any real preheat calculation. It carries an "engineering estimate" badge in the tool for that reason. Use it to decide whether preheat is a question for your joint, and take the actual temperature from EN 1011-2 Annex C, your consumable manufacturer's data, or a qualified welding procedure.

Because a full-penetration butt weld cannot be stronger than the section it joins. For that weld type the throat plane IS the parent cross-section, so the calculator caps the resistance at the plate's yield strength as well as applying the EN 1993-1-8 throat limits, and tells you when the parent metal is what governs. It matters most where the ratio of ultimate to yield strength is large: for 304 stainless (fu 540 MPa, fy 210 MPa) the parent cap is well below the weld-metal limit, so a joint that would pass on weld strength alone can still be inadequate.

You can run it during a free 30-minute preview with no sign-up required. A free 14-day account trial unlocks every calculator with no credit card. The branded PDF engineering report and saved calculations are included in the free 14-day trial and in every paid plan.