Welding symbol builder
Assemble a symbol from its parts — the tool draws it and explains every element in words. Switching between ISO 2553 and AWS A2.4 shows the main divergence between the systems: the same picture means a different side of the joint.
What a symbol is made of
The arrow points at the joint. Where the joint is asymmetric — a single-bevel preparation, for instance — the arrow points at the member that gets prepared, and it is bent to make that unambiguous.
The reference line carries everything else. In ISO system A there are two: a continuous line and a dashed one. In AWS there is one, and the side is given by whether the symbol sits above or below it.
The elementary symbol is the shape of the weld: a triangle for a fillet, a V for a single-V butt, a square for a square butt, a half-V for a single bevel, a U or J for those preparations.
Dimensions sit either side. On the left, the size —
a5 for a 5 mm throat, z7 for a 7 mm leg. On
the right, the length and, for an intermittent weld, the spacing (ISO) or the pitch (AWS).
The tail holds the process number, the WPS reference or the
quality level. A tail marked 141 means TIG, from
EN ISO 4063.
| Element | Where it sits | What it sets |
|---|---|---|
| Arrow | The start of the leader line | Points at the joint and fixes the arrow side |
| Reference line | Horizontal | Carries every other element |
| Identification line | Dashed, parallel to the reference line | ISO only, system A: the other side |
| Symbol | On the line | The weld type |
| Left of the symbol | — | Size: a — design throat, z — leg length |
| Right of the symbol | — | Length, the number of runs and the gap between them |
| Circle at the elbow | — | A weld all round the joint |
| Flag at the elbow | — | A site weld |
| Tail | The end of the line | The process to ISO 4063, the WPS, the quality level |
The three things that get misread
a and z. a5 is a throat of 5 mm;
z5 is a leg of 5 mm, which is a throat of only 3.5. Reading one
as the other is the most expensive mistake on this page — the conversion is in
the fillet weld
calculator.
Which side. Get the system wrong and you weld the wrong face. If a drawing shows a dashed reference line, it is ISO; if the symbol sits above or below a single line, it is AWS. The differences are set out in ISO 2553 and AWS A2.4.
The flag and the circle. Both live at the elbow of the arrow and they mean different things: circle is all-round, flag is a field weld. A drawing can carry both.
The full reading order, from arrow to tail, is in how to read welding symbols.
Building a symbol, field by field
The builder's fields come in the same order in which a symbol is read on a drawing. Fill them from top to bottom:
- Symbol system. ISO 2553 for European drawings, AWS A2.4 for American ones. Switching with the same settings shows how one intention is written in both systems.
- Weld type. Fillet for T-joints, laps and corners; square, single-V, single-bevel, U and J for butts; plus backing run, plug and spot.
- Side. Arrow side, other side or both. This is where most misreadings start, so switch it back and forth and watch where the symbol moves.
- Dimension on the left. Type it as it appears on the
drawing, with its letter:
a5,z7, ors6for a partial-penetration butt weld. A bare number with no letter in ISO mode is asking for trouble. - Dimension on the right.
200for a continuous weld 200 mm long; leave it empty for a weld along the whole joint. Intermittent:3×50 (100)in ISO,50-150in AWS. - Surface finish. Flush, convex or concave — only when the contour matters, for fatigue or because another part has to sit tight on the weld.
- Process in the tail. 111, 135 or 141 to ISO 4063.
- All round and field weld. Circle — all the way round the closed outline; flag — made on site.
Under the drawing the builder spells out every element in words. Read that list against what you meant to specify: if something does not match, the mistake is in the settings, not the drawing. The "Share this calculation" button copies a link with the current settings, so the symbol can be sent to a colleague for checking.
Four ready-made examples to rebuild
- T-joint welded both sides. ISO, fillet, both sides,
a4, length empty, process 135. Result: two a4 fillets along the whole joint, MAG with solid wire. - Butt joint in 10 mm plate. ISO, single-V, arrow side, no dimension (full penetration), process 111. Add the root run from the other side as a second symbol: backing run, other side.
- Stiffener on an intermittent weld. ISO, fillet, arrow
side,
a3,4×60 (120). The weld occupies 4·60 + 3·120 = 600 mm and contains 240 mm of weld. Switch to AWS and type60-180— the same geometry. - Column erected on site. ISO, fillet, arrow side,
a6, "weld all round" and "field weld" ticked, process 135.
What the builder does not do, and what to add by hand
- One size for both sides. An asymmetrical weld is built from two symbols (see the questions below).
- Three processes. The tail offers 111, 135 and 141. Flux-cored wire (136), submerged arc (121) and other numbers go on the drawing by hand — the full list is in the process number table.
- No quality level or position. On a production drawing the
tail usually also carries the quality level to
ISO 5817 and the
position to ISO 6947, e.g.
135/ISO 5817-C/ISO 6947-PB. - No groove dimensions. Angle, gap and root face for butt welds come from the WPS or the preparation standard — see joint preparation.
From joint to symbol: the order of decisions
The builder helps you draw, but the decisions come first. The order that saves rework:
- Joint type — T, lap, butt, corner.
- Weld type — for a butt joint thickness decides: square butt up to about 3–4 mm, single-V to about 12 mm, thicker plate double-V with access from both sides or U from one side (figures from the joint preparation table).
- Size — for a fillet, a from the design or the calculator; remember that the cross-section grows with the square of a.
- Side and length — where the access is and whether the weld has to be continuous.
- Shop or site, all round or a segment — the flag and the circle.
- Tail — process, quality level, position, WPS number.
Frequently asked questions
Why does ISO 2553 have two lines and AWS only one?
Because the two systems answer "which side" differently. ISO 2553 system A draws a continuous line with a dashed line parallel to it: a symbol on the continuous line means the arrow side, one on the dashed line means the other side. AWS A2.4 manages with one line and uses position instead — below the line is the arrow side, above it is the other side. The second is more compact, the first is harder to misread.
What does the circle at the elbow of the line mean?
That the weld runs all the way round a closed contour: around a pipe, around the outline of a doubler plate, around a flange. Without it the weld is made only where the arrow points. A flag in the same place means something else entirely — a field weld, made on site rather than in the shop.
How is an intermittent weld written?
To the right of the symbol: number of segments, multiplication sign, segment length, and the spacing in brackets. 3×50 (100) means three 50 mm segments with 100 mm spaces, measured from the end of one segment to the start of the next (ISO 2553; in AWS the same weld is 50-150). The size of the weld itself stays on the left of the symbol.
Can I copy the finished symbol onto a drawing?
As a teaching example, yes. As a production drawing element, no: a real drawing usually also needs the quality level to ISO 5817, the welding position and a reference to the WPS, and the drafting itself follows company conventions. This tool answers "how is this read", it does not replace design documentation.
How do I enter an intermittent weld in AWS mode?
Type the segment length and the pitch separated by a hyphen in the length field, for example 50-150. AWS measures the pitch centre to centre, so this is the same weld that ISO mode writes as 3×50 (100). AWS does not state the number of segments; it follows from the joint length.
How do I show a double-sided weld with different sizes on each side?
The "both sides" option draws both sides with one size — a symmetrical weld. For an asymmetrical one, say a5 on the arrow side and a3 on the other, build two symbols in turn — "arrow side" with a5 and "other side" with a3 — and combine them on one reference line with its dashed line on the drawing.
Updated: