Welding Symbols Explained: How to Read Weld Symbols on Steel Drawings
STRUCTURAL STEEL · DRAWING REFERENCE
Welding symbols communicate where a weld belongs and what the drawing requires. For structural drafters, the challenge is often practical: identifying the correct joint, choosing the right side of the reference line, and checking that the symbol agrees with the section detail.
This guide covers common AWS-style notation used on U.S. drawings, with original examples you can compare while reviewing a detail.
1. Understand the parts of a welding symbol
The horizontal reference line carries the instructions. The arrow identifies the joint. A basic weld symbol, such as a fillet triangle, identifies the weld type. The optional tail can refer to a process, specification, or detail.
Strictly speaking, the weld symbol is one element of the complete welding symbol. That distinction helps when discussing a correction: are you changing the weld type, or the entire callout?
2. Arrow side vs. other side
| Symbol location | AWS-style interpretation |
|---|---|
| Below the reference line | Arrow side of the indicated joint |
| Above the reference line | Other side of that joint |
| Above and below | Both sides, with the requirements shown for each |
Below does not mean the physical bottom of the steel. It identifies the arrow side even if the leader points upward or approaches the joint from a different direction.
The joint matters as much as the symbol. A both-sides callout on one plate-to-member joint does not automatically apply to another plate on the opposite face of the member. For complicated HSS or slotted-plate details, use sections and explicit joint identification rather than assuming “both sides” covers every exterior weld.
3. Read fillet weld size and length separately
For a typical equal-leg fillet weld, the number to the left is the specified leg size. A length, when provided, appears to the right. Figure 1 reads as a 1/4-inch fillet weld, 4 inches long, on the arrow side.
Do not read 1/4 as the plate thickness or the weld throat. Also confirm drawing units before interpreting a bare number. This article’s numerical examples use inches.
A specified length does not necessarily locate its start and end along a longer joint. Add dimensions or a detail where placement matters. When no length is shown, determine the required extent from the joint geometry and the applicable drawing instructions; do not assume it means a short tack weld.
4. Intermittent welds: length is not pitch
Intermittent fillet welds use separated segments. The notation 2–6 gives a 2-inch segment length and a 6-inch center-to-center pitch.
In this example, adjacent equal-length segments have a 4-inch clear gap. Reading the second number as the gap would place the welds too far apart. The complete drawing still needs to establish where the pattern begins, ends, and applies.
For two-sided intermittent welds, distinguish a chain arrangement from a staggered arrangement. Do not simply mirror a one-sided callout in your CAD model. Show the intended pattern and the requirements for each side.
5. Field weld and weld-all-around symbols
The flag identifies welding to be performed in the field. It is worth checking the flag against the erection sequence: can the crew reach the joint after the members are installed?
The circle at the arrow/reference-line junction indicates welding all around the indicated joint. It does not mean “weld every edge on this assembly.” A circle elsewhere in a welding symbol can have a different meaning; placement is essential.
For a tube-to-plate connection, a plan or section should make the intended weld path clear. “Both sides” and “all around” are not interchangeable instructions.
6. Recognize common weld types
| Type | What to recognize | Detail to verify |
|---|---|---|
| Fillet | Right-triangle symbol | Joint side, leg size, and extent |
| Square groove | Two parallel strokes | Root opening and joint requirements |
| V-groove | Two inclined strokes | Preparation of both edges |
| Bevel groove | One vertical and one inclined stroke | Which member receives edge preparation |
| U- or J-groove | Curved groove profile | Prepared geometry and supporting detail |
For certain groove symbols, a break in the arrow identifies the member to be prepared. Treat the leader as meaningful drafting information, not merely a convenient line to route around text.
7. A symbol is not a complete connection design
Recognizing the symbol does not establish that the weld can carry the required force. Keep three tasks separate during a review:
- Interpretation: what does the drawing specify?
- Design: does that weld and the connected material have adequate strength?
- Execution: can the joint be prepared, welded, and inspected as required?
CJP means complete joint penetration; PJP means partial joint penetration. If either appears in a detail, review the specified penetration and complete joint detail. Do not infer the entire groove-weld requirement from a V-shaped mark alone. Likewise, a finish instruction must agree with the intended surface contour and project requirements.
Practical drawing-review examples
Example A: a stiffener welded to a beam web
First identify the stiffener-to-web joint. Then check whether one or both sides are called out. Finally, compare the specified weld extent with the stiffener length and corner clearances. The flange connection is another item to resolve; a symbol aimed at the web joint should not silently define it.
Example B: a connection moved from shop to field
Do more than add a flag. Coordinate access, erection sequence, nearby bolts, coatings, and inspection requirements. A drafting change that looks minor can change how the connection is built.
Example C: a copied detail with different units
Read the source detail’s unit system before copying the callout. Converting a dimension and selecting an appropriate nominal metric weld size are different decisions. Do not replace 1/4 inch with an arbitrary whole-number millimeter value without checking the design.
Quick checklist before issuing a detail
- Does the arrow terminate at the intended joint?
- Is the basic symbol on the correct side of the reference line?
- Are sizes and units clear?
- Are length, pitch, and weld extent unambiguous?
- Are field and all-around instructions intentional?
- Do the section view, notes, and callout agree?
- Is the specified weld physically accessible?
- Have conflicting or incomplete instructions been resolved?
Frequently asked questions
Does a triangle above the line mean an overhead weld?
No. In the AWS convention discussed here, it indicates a fillet weld on the other side of the joint. It does not specify the welder’s working position.
Does 2–6 mean two welds that are six inches long?
No. For the intermittent fillet example, it means 2-inch-long segments at 6-inch pitch.
Can I use this guide for every international drawing?
Check the stated symbol standard first. This guide uses AWS-style notation. Do not apply its reference-line rules blindly to a drawing using another convention.
Key takeaway
Locate the joint before interpreting the symbol. Then read the side, type, size, extent, and additional instructions in a consistent order. A clear section and an accurate arrow often prevent more confusion than adding another general note.
Scope: practical symbol-reading reference, not a complete symbol catalog or weld design procedure. Original illustrations are schematic and not to scale. Example sizes are for reading practice only. Follow the project’s specified standards, approved details, and welding procedures.
Technical references
- AWS A2.4:2020, Standard Symbols for Welding, Brazing, and Nondestructive Examination; consult the edition specified for your project.
- Miller Electric, “How to Read and Understand Weld Symbols” and Welding Symbol Chart.
- National Board of Boiler and Pressure Vessel Inspectors, “Welding Symbols: A Useful System or Undecipherable Hieroglyphics?”
- Steel Tube Institute, “Full-Capacity Welds: CJP vs. Fillet vs. Fillet-Reinforced PJP.”
- Chris Thurow, “How to Correctly Use Welding Symbols for Slotted Hollow Structural Steel Members,” AWS Inspection Trends, May 2025.
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