Weld size and weld metal
Single-V butt weld cross-section and weld metal mass
- where
- cap width (mm)
- root gap (mm)
- plate thickness (mm)
- root face (mm)
- included bevel angle (°)
- weld cross-section area (mm²)
- cap height (mm)
- weld metal mass per metre (kg/m)
- weld metal density (kg/m³)
- total weld metal mass (kg)
- total weld length (m)
Explain this equation
Works out the cross-section and weld metal of a single-V butt weld from the joint preparation. Use it for estimating wire and time, or comparing preparations.
The gap g runs the full plate thickness, giving a rectangle g × t. Above the root face c each plate is bevelled at half the included angle, so each side opens by (t − c) tan(α/2); the two triangles together make (t − c)² tan(α/2). The cap width w is the gap plus both bevels at the top, and a parabolic cap of height h adds two-thirds of w × h. Mass follows from area times density.
The prep is split into a rectangle, two triangles and a cap, and their areas added.
Sense check: 10 mm plate, 60° included, 2 mm gap and 1.5 mm root face gives about 62 mm² without cap, about 0.48 kg per metre.
Watch out: weld metal rises roughly with the square of thickness and with the bevel angle. A smaller angle saves wire but must still give access to fuse the sidewalls.
Works out the weld metal in a single-V full-penetration butt weld from the joint preparation: plate thickness, included angle, root gap, root face and cap height.
Enter your values to see the result.
Good to know
The area is the gap strip across the full thickness, plus the two bevel triangles above the root face, plus a parabolic cap over the groove width w. A 10 mm plate, 60°, 2 mm gap and 1.5 mm root face holds about 0.48 kg/m before the cap. Root penetration bead and cap overlap onto the plate surface are not included.
Common mistake
Using the bevel angle of one plate (e.g. 30°) instead of the included angle (60°). This halves the bevel area.
Limits
Symmetrical single-V preparation, full penetration, flat cap modelled as a parabola. For double-V, J or U preparations work each part separately.
Sources
- Kiwa: ISO 5817 quick guide (excess weld metal 502 and excessive convexity 503: h ≤ 1 + 0.25b / 0.15b / 0.1b for levels D / C / B; fillet maxima 5 / 4 / 3 mm)
- BS EN ISO 5817:2023 Welding – Fusion-welded joints in steel, nickel, titanium and their alloys – Quality levels for imperfections
- BS EN ISO 2553:2019 Welding and allied processes – Symbolic representation on drawings – Welded joints (a = throat thickness, z = leg length)
- BS EN 1991-1-1:2002 Eurocode 1, Annex A: nominal density of steel 77.0–78.5 kN/m³ (7850 kg/m³ is the usual design value)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the welding procedure specification (WPS), BS EN ISO 15614/9606, BS EN 1090, BS EN 1993 and manufacturers’ data. Structural welds need qualified welders and engineered designs.