Weld Symbols Explained: Chart, Meanings, and How to Read Them
If you’ve ever looked at a welding blueprint, you’ve probably seen arrows, triangles, lines, and numbers around each joint. These weld symbols are a standardized way for designers, engineers, and welders to communicate what type of weld is required, where it goes, and how it should be made.
This guide explains the most common weld symbols and their meanings, with a weld symbol chart for quick reference. You’ll also learn the differences between AWS and ISO symbols, what each part of a welding symbol means, and how to read welding symbols on a blueprint step by step.
Weld Symbols Chart And Meanings
An engineering drawing is a concise version of a physical part, with dimensions drawn to scale. Welding information is conveyed the same way, through symbols.
Welding symbols are a standardized language for the joint, weld type, and its specifications (such as size, position, and welding process).
Here's a reference chart you can use in your own workshop. It is drawn from the actual chart specified in AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination.
Weld Symbols vs Welding Symbols
Weld symbols and welding symbols are typically used synonymously. However, technically they mean something different.
As per AWS A3.0:2020, a welding symbol is the complete graphical representation of the specifications for producing a welded joint, and it requires at minimum a reference line and an arrow. In contrast, a weld symbol is an individual graphic character attached to that reference line specifying the joint geometry or weld type.
Referring back to the chart above, the triangle used to call out a fillet weld is a weld symbol. The full drawing around it (reference line, arrow, and every other element included) is the welding symbol.
AWS vs. ISO Welding Symbols
Two major standards are used for welding symbols: AWS A2.4, widely used in North America, and ISO 2553, commonly used internationally. ISO 2553 includes two notation methods, System A and System B.
The basic elementary symbols largely resemble each other, but the core difference is in how side-of-joint designation is indicated on the reference line:
AWS A2.4 (and ISO 2553 System B) use a single reference line. A weld symbol below the line indicates the arrow side; a symbol above the line indicates the other side.
ISO 2553 System A uses two reference lines, one solid and one dashed. Symbols on the solid line indicate the arrow side, while symbols on the dashed line indicate the other side.
Quick way to spot: A dashed line running alongside the reference line on a print, that’s definitely ISO. If not, it could be either AWS or ISO.
Parts of a Welding Symbol and Common Supplementary Symbols
A welding symbol combines several elements to show where, what, and how to weld. The diagram below shows the main parts of an AWS welding symbol, followed by a breakdown of what each one means.
You don’t have to be intimidated by this complex diagram, as we will break it down and study each weld symbol individually.
Reference Line
The reference line is the horizontal baseline of a welding symbol. Weld symbols, dimensions, supplementary symbols, and the tail are positioned relative to this line.
Arrow: Arrow Side vs. Other Side
The arrow points to the joint to be welded. Under AWS A2.4, a weld symbol below the reference line indicates the arrow side; a symbol above the line indicates the other side. If symbols appear on both sides of the line, both sides of the joint are to be welded.
Tail
The tail is presented at the opposite end of the reference line (from the arrow). That’s space for placing process notes, specification references, or welding procedure numbers, or anything that doesn't have a defined position elsewhere on the symbol. The tail is optional and used for process notes, specifications, or procedure references.
Flag: Field Weld vs. Shop Weld
A flag at the junction of the arrow and reference line indicates a field weld, meaning the weld is to be made on site. If no flag is shown, the weld is generally made in the shop unless the drawing or project requirements specify otherwise.
Field welding may involve wind, temperature changes, limited access, and portable equipment, while shop welding is typically performed under more controlled conditions.
All Around Symbol
This symbol is also located on the junction of the reference line and arrow. An open circle indicates the weld should continue around the joint. It is commonly prescribed for pipe-to-plate connections, tube frames, or a part where the joint wraps around a perimeter. This does not necessarily mean welding every side of the entire part. It means the weld continues around the joint or connected joint perimeter identified by the arrow.
Numbers/Dimensions
Weld dimensions are placed adjacent to the weld symbol, with their position indicating the type of measurement. For fillet welds, the convention is as follows:
- Size (leg): shown to the left of the symbol
- Length: shown to the right
- Pitch (intermittent welds): indicated as as length–pitch (to the right)
For groove welds, measurements follow this pattern:
- Depth of bevel or weld size: show to the left of the symbol
- Effective throat: in parentheses to the left (when specified)
- Root opening: inside the symbol
- Groove angle: open end of the symbol
More dimensional details have been added in the section explaining each weld symbol individually, or you can refer to our main diagram.
Weld Contour Symbols: Convex, Concave, and Flush
Contour symbols describe the finished shape of the weld face; it’s represented by a small line sitting above the weld symbol. A straight horizontal line means the weld requires a flush, flat finish. A curve bulging outward calls for convex. A curve dipping inward means concave.
Next to the contour symbol, sometimes there’s a single letter written next to it: G for grinding, M for machining, C for chipping, H for hammering, R for rolling. That letter tells the welder how to achieve the contour. No letter means the contour should come out that way as-welded.
Basic Weld Symbols: Fillet, Groove, Plug, Spot, Seam, and Stud
Welds come in different forms, and each one is designated through its own symbol. Here's a guide to the common weld joint types you'll run into on any welding symbols chart.
Fillet Weld Symbol (Triangle Shape)
The fillet weld symbol is a right triangle that sits on the reference line; the right angle touches the line itself. One of the most common symbols you'll see for T-joints, lap joints, and corner joints.
For fillet welds, leg size appears to the left, weld length to the right, and pitch (for intermittent welds) after a dash.
Note: For fillet, groove, plug/slot, spot, and seam welds, placement on the reference line follows the same side convention: below the line means arrow side and above means other side.
Groove Weld Symbols (Square, V, Bevel, U, J, Flare)
Groove welds join pieces edge to edge, typically in butt joints, though they also show up in corner, T, and edge joints. Each groove type reflects how the edges were prepared before welding:
- Square groove: No edge preparation, used mainly on thinner material.
- V groove: Both pieces beveled, forming a V. Common on thicker material that needing full penetration weld.
- Bevel groove: Only one piece beveled, the other left square. Has a cheaper prep, since only one edge needs machining.
- U groove: Both pieces machined with a concave radius. This groove reduces weld volume and distortion on thick sections, at the cost of more expensive prep.
- J groove: One piece is machined concave, the other is left square. It has the same benefit as a U-groove, with less prep work.
- Flare-V and flare-bevel groove: It is used when the parts themselves are curved or round, like tube-to-tube or tube-to-plate. The natural curvature forms the groove instead of a machined edge.
Plug and Slot Weld Symbol
Plug and slot both use the same weld symbol, a rectangle placed above or below the reference line. The difference is in the part itself. A plug weld fills a round/circular hole, whereas a slot weld fills an elongated (long and narrow) one.
In the case of a plug weld, hole diameter appears on the left of weld symbol. For slot weld, the width is to the left of the rectangle while its length and pitch appear to the right. For both welds, the depth of fill is written inside the rectangle, and the arrow or other side placement indicates which member contains the hole.
*Note: In the latest AWS A2.4 edition, the diameter symbol, $\varnothing$ was removed from the plug weld icon itself, but it remains required in the dimension string to signify diameter)
Spot Weld Symbol
The spot weld symbol is a plain circle. It is used to join overlapping pieces at individual points, either by resistance welding or arc spot welding (whatever is specified in the tail).
If the circle is centered directly on the reference line instead, the side doesn't matter; you can weld from whichever side is more accessible.
Size is mentioned to the left of the symbol. The number of spot welds required is written in parentheses, above or below the symbol depending on where the symbol itself is.
Seam Weld Symbol
The seam weld symbol looks like the spot weld circle, but with two parallel lines running through it. It is used for overlapping joints that need welding along a line rather than at individual points. Seam welds may be continuous or intermittent and are commonly used where consistent joining or sealing is required.
Width is written to the left of the symbol, length to the right, and pitch after that if multiple seam segments are specified.
Stud Weld Symbol
The stud weld symbol is a circle with an X through it. It calls out a metal stud welded onto a flat surface, usually with a dedicated stud welding gun.
Unlike most other symbols, stud welds only ever appear on the arrow side. There's no other-side version. Diameter, number of studs, and spacing follow the same placement conventions as spot and seam welds.
How to Read Welding Blueprint Symbols?
When reading a welding symbol on a blueprint, work through it in the same order each time: joint location → weld type and side → supplementary symbols → dimensions → process notes.
1. Locate the reference line and arrow. Find the horizontal reference line first, then follow the arrow to the actual joint on the part.
2. Read the weld symbol on the line. Check whether it sits below the line (arrow side), above it (other side), or both. The shape itself (triangle, V, circle) tells you the weld type.
3. Check for supplementary symbols. Look at the arrow-reference junction for a flag (field weld) or open circle (weld all around). Check above the weld symbol for a contour mark.
4. Read the dimensions. Check the values around the weld symbol for weld size, length, pitch, and any groove dimensions. For example, fillet-weld size is shown to the left, while length and pitch appear to the right. Groove welds may also specify depth of bevel, effective throat, root opening, and groove angle.
5. Check the tail. If a tail is present, it carries process notes, i.e., what type of welding process to use, WPS references, or other specs not covered elsewhere on the symbol. If there’s no tail, that means no extra information beyond what's already shown.
For example, a fillet weld symbol below the reference line with 1/4 on the left and 2–6 on the right means:
- Fillet weld — indicated by the triangle.
- Arrow side — because the symbol is below the reference line.
- 1/4 in. leg size — shown to the left.
- 2 in. weld length at 6 in. pitch — shown to the right.
Turning Weld Symbols Into Accurate Fabrication
Understanding weld symbols is fundamental to entering professional welding. However, interpreting a symbol correctly alone does not guarantee an accurate final assembly. The symbol must be translated into part geometry, joint preparation, feature placement, fit-up, welding execution, and inspection.
Digital cutting and marking address this gap by reducing repeated layout work and standardizing how features are transferred from the drawing to the part. Joint edges, hole locations, and weld positions can be cut or marked directly, which improves consistency between parts and minimizes cumulative error across batches.
An integrated system such as xTool MetalFab brings these steps into a single workflow. It functions as a CNC laser cutting and engraving platform, allowing parts to be cut to geometry and marked for alignment in the same setup. With a handheld laser welding module, those marked joints can then be welded at the intended locations without re-referencing. This continuity helps maintain dimensional accuracy from initial layout through final assembly.
Conclusion
Weld symbols are the bridge between a drawing and the work done at the joint. Once you understand them, reading any print becomes as routine as any other shopping task. Keep a weld symbols chart nearby, printed and pinned up in your workshop. Next time you hit a symbol you don't recognize, match it and get back to work.
FAQs
1. What does a dashed line mean on a weld symbol?
It defines ISO 2553 (System A) notation. That dashed line is actually a second reference line, used specifically to designate a weld on the other side of the joint (while the solid line indicates the arrow side).
2. What is the symbol for a back weld?
A back weld uses the same unshaded half-circle symbol as a backing weld, placed on the opposite side of the reference line from the main weld. The tail specifies which type exactly it is because the shape alone doesn't distinguish them. Practically, a backing weld is made before the main weld to support the root pass, while a back weld is made after the main weld.
3. What Is a Weld Callout or Welding Notation?
A weld callout, or welding notation, is the complete symbol on a drawing that specifies a weld: reference line, arrow, weld symbol, and any dimensions or supplementary marks attached to it. It's another name for what AWS defines as the welding symbol.
4. Where Can I Download a Printable Weld Symbol Chart?
Use the reference chart earlier in this guide. It is made directly from the AWS A2.4 chart and set up for printing and shop use. Or you can download the official chart from AWS.
5. Do I need special software to turn a welding drawing into a cut or engrave file?
Yes, a welding drawing is made to be read as a design guide. So it needs to pass through vector design or CAD/CAM software to become a cut or engrave file.
6. Can you mark weld symbols directly onto metal before fabrication?
Yes. Weld locations, alignment lines, and fabrication references can be marked directly onto metal before welding. For one-off work, this may be done with soapstone or metal markers; for repeatable digital fabrication, laser marking can transfer reference lines or identifiers onto parts more consistently.
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