Weld Symbol Chart — AWS A2.4 & ISO 2553 Complete Reference

This page is a complete reference for welding symbols used in structural steel detailing and fabrication drawings. It covers the American Welding Society AWS A2.4 standard (used in the United States, Canada, and many international projects with North American engineering firms) and the ISO 2553 international standard (used in Europe, the UK, Australia, and much of Asia). Every weld symbol described below is keyed to the applicable standard clause, with notes on differences between the two systems that have caused costly fabrication errors on international projects.

Welding symbols communicate four essential pieces of information that a welder needs: (1) the type of weld (fillet, groove, plug, slot, spot, seam, stud, or edge), (2) the location of the weld relative to the arrow (arrow side, other side, or both sides), (3) the dimensions — size, length, pitch, effective throat, and root opening, and (4) supplementary requirements — field or shop weld, all-around, contour, finish method, backing, and melt-through.

A correctly placed welding symbol eliminates ambiguity. A missing symbol or a symbol placed on the wrong side of the reference line has led to welds being deposited on the wrong face of a joint, requiring expensive rework. This reference ensures you get every symbol right the first time.

Weld Symbol Chart — Common Welding Symbols

The table below lists the most common welding symbols per AWS A2.4 with their arrow-side, other-side, and both-sides configurations. The "Symbol Shape" column describes what the welder sees on the drawing. The remaining columns explain where the symbol is placed relative to the reference line and what that placement means for the joint.

How to read the symbol placement: The horizontal reference line is the anchor. Everything below the reference line applies to the arrow side of the joint. Everything above the reference line applies to the other side (the side opposite the arrow). A symbol placed on both sides of the reference line (straddling it) means weld both sides. The arrow connects the reference line to the joint. The tail at the opposite end of the reference line (when present) carries the welding process specification, filler metal, or other notes.

Arrow Side vs. Other Side — The Fundamental Convention

The arrow-side / other-side convention is the single most important rule in welding symbology and the one most frequently misinterpreted. Get this right, and the rest follows.

Arrow side: The side of the joint that the arrow physically points to. Imagine the arrow tip touching the member to be welded. The weld symbol placed BELOW the reference line (closer to the arrow) specifies the weld on this side. For a fillet weld, a triangle below the reference line tells the welder: "Deposit a fillet weld on the side the arrow points to."

Other side: The opposite side of the joint — the side NOT pointed to by the arrow. The weld symbol placed ABOVE the reference line specifies the weld on this side. A triangle above the reference line tells the welder: "Deposit a fillet weld on the side opposite where the arrow points."

Both sides: When the same weld symbol appears both above and below the reference line, the same weld is made on both sides of the joint. For a double-sided fillet weld, this appears as a triangle both above and below the reference line. If the fillet size differs between the two sides, different numbers appear to the left of each triangle.

Arrow-side significance for groove welds: For single groove welds, the arrow side DOES matter because it indicates which member is beveled. Point the arrow to the member that will receive the bevel preparation. The member NOT pointed to by the arrow remains square-cut (for single-bevel and single-J) or receives the opposite bevel. For double groove welds (V both sides = X-groove, bevel both sides = K-groove), the arrow side convention still applies to identify which member gets which preparation.

Fillet Weld Symbol — Dimensions and Their Position

The fillet weld symbol is the right triangle placed on the reference line. The dimensions are placed in specific positions relative to the symbol, and each position has a specific meaning:

• Size (leg length): Placed to the LEFT of the fillet symbol. For equal-leg fillets, this is the leg dimension in inches or millimeters (e.g., 1/4, 5/16, 3/8, or 6 mm, 8 mm). For unequal-leg fillets, both leg dimensions are shown separated by a multiplication sign (e.g., 3/8 x 1/4 means a 3/8-inch vertical leg and a 1/4-inch horizontal leg).
• Length: Placed to the RIGHT of the fillet symbol. If no length is shown, the weld runs the full length of the joint. Intermittent fillets show the length of each individual weld segment (e.g., 3 for a 3-inch-long weld).
• Pitch: The center-to-center spacing of intermittent fillet welds, placed to the right of the length after a hyphen. For example, 3-12 means a 3-inch-long fillet weld segment repeated at 12-inch centers. The unwelded space between segments is 12 - 3 = 9 inches.
• Contour and finish: Shown above the fillet symbol. A straight horizontal line means the weld face must be finished flat (flush with the base metal). An upward-arcing curve means the weld face is finished convex (bulging outward, which is the as-welded condition for most fillets). A downward-arcing curve means the weld face is finished concave (dished inward). The finish method letter follows the contour symbol: G = grinding, M = machining, C = chipping, H = hammering, F = forging, U = method unspecified.
• Field weld flag: A small flag (pennant shape) at the junction of the arrow and the reference line means the weld is made in the field (at the job site), not in the fabrication shop. The absence of a flag means the weld is made in the shop under controlled conditions.
• Weld-all-around circle: A small circle at the junction of the arrow and the reference line means the weld continues around the entire perimeter of the joint without interruption.

Complete fillet weld symbol example: A 5/16 fillet weld, 3 inches long at 12-inch centers, on the arrow side, field welded, ground flat would show: 5/16 to the left of the triangle, 3-12 to the right, a straight line (flat contour) above the triangle with G (grinding finish), and a field weld flag at the arrow-reference line junction. This tells the welder everything needed to make the weld correctly the first time.

Groove Weld Symbol Reference

Groove welds join members in the same plane by filling a prepared groove between them. The groove type is selected based on plate thickness, welding position, access, and cost. The table below covers all six standard groove types per AWS A2.4, with CJP and PJP variants, backing requirements, and preparation notes.

CJP vs. PJP designation: A Complete Joint Penetration (CJP) groove weld has the weld metal fully penetrating the joint thickness — the weld is as strong as the base metal. A Partial Joint Penetration (PJP) groove weld has the weld metal penetrating only part of the joint thickness. CJP welds are specified by adding "CJP" in the tail. PJP welds show the required effective throat dimension to the left of the groove symbol. The effective throat for a PJP groove weld is the minimum distance from the weld face to the weld root, excluding any reinforcement.

When to use each groove type:

• Square groove: Fastest and cheapest — no edge preparation. Use for sheet and thin plate up to 1/4 inch (6 mm) for CJP with backing, or up to 5/16 inch (8 mm) with a root opening and backgouge.
• Single V-groove: The workhorse for plate butt joints from 1/4 inch to 2 inches thick. 60 degrees included angle is standard. Bevel both members 30 degrees each. Weld metal volume grows with the square of thickness — for thicknesses over 1-1/2 inches, consider double V to reduce weld metal.
• Double V (X-groove): Halves the weld metal volume compared to single V for the same thickness. Alternate welding passes from side to side to balance shrinkage and control angular distortion. Requires access to both sides.
• Single bevel: One member beveled, one square. Faster to prepare than V (only one member machined). Common for T-joints and corner joints.
• U-groove and J-groove: Lowest weld metal volume for thick sections (>= 2 inches) but highest preparation cost (machining). Used in heavy fabrication (pressure vessels, bridge girders, heavy columns) where weld metal savings justify the machining cost.

Supplementary Weld Symbols

Supplementary symbols modify the base weld symbol with additional requirements. They are placed at specific locations around the reference line and arrow junction. The table below covers all standard supplementary symbols per AWS A2.4.

Field Weld Symbol — Detailed Guidance

The field weld flag (a blackened pennant-shaped flag at the arrow-reference line junction) instructs the fabricator that this weld is to be made at the construction site, not in the fabrication shop. This distinction matters for several reasons:

• Sequence: Field welds are made after erection and alignment. The erection sequence must provide access for the welder to reach the joint. A field weld at a column splice at the 20th floor requires a different access plan than a shop weld at a beam-to-column flange connection fabricated at ground level.
• Quality: Field welds are made in less controlled conditions (wind, temperature, humidity, position) than shop welds. Welding procedure specifications (WPS) for field welds often require preheat even for thicknesses that would not need it in the shop, and low-hydrogen electrodes are standard.
• Inspection: Field welds typically receive more extensive nondestructive testing (NDT) than equivalent shop welds. UT (ultrasonic testing) or RT (radiography) of field CJP groove welds is standard on most structural projects.
• Cost: Field welding typically costs 2-4x more than shop welding per pound of deposited weld metal, accounting for access equipment, weather protection, position welding productivity loss, and inspection.

No flag = shop weld. If a weld symbol has no flag, it is assumed to be a shop weld. Never assume a field weld — always specify it explicitly.

Weld-All-Around Symbol — Applications

The weld-all-around circle instructs the welder to continue the specified weld around the entire perimeter of the joint without starting or stopping at corners. Common applications:

• HSS column base plate: A fillet weld all around the HSS perimeter connects the column to the base plate. The circle eliminates ambiguity about whether the inside corners of a rectangular HSS or the full circumference of a round HSS is to be welded.
• Pipe-to-flange joints: Full-penetration groove weld all around the pipe circumference at a flange connection.
• Bracing connection gussets: Gusset plates welded to beams and columns at brace connections often receive a fillet weld all around for full force transfer.
• Box section splices: CJP groove weld all around the box section perimeter at a column or chord splice.

The all-around symbol does not mean "weld everywhere on the drawing" — it applies only to the specific joint that the arrow points to. For multiple joints, each requires its own all-around symbol.

Contour and Finish Symbols

Contour symbols specify the required shape of the finished weld face. This is separate from the as-welded profile — contour symbols indicate post-weld finishing operations:

When contour matters: Contour is primarily a fatigue consideration. A flat (ground flush) weld face at a CJP groove weld removes the stress concentration at the weld toe, improving the fatigue category from Category C to Category B (AISC 360 Appendix 3, Table A-3.1). This is required for tension flanges in bridge girders, crane runway girders, and dynamically loaded structures. For statically loaded building connections, contour specifications are rare.

AWS A2.4 vs. ISO 2553 — Key Differences

The two dominant welding symbol standards — AWS A2.4 (American Welding Society) and ISO 2553 (International Organization for Standardization) — agree on about 80% of symbology but differ on the 20% that causes most interpretation errors. The table below catalogs every significant difference.

The most dangerous difference — reference line interpretation:

In AWS A2.4, symbols BELOW the reference line apply to the arrow side. In ISO 2553, symbols ON the SOLID reference line apply to the arrow side, and symbols ON the DASHED reference line apply to the other side.

If a drawing uses ISO 2553 symbols but the welder is trained on AWS A2.4 (or vice versa), the welder may deposit welds on the wrong side of the joint. This has happened on international projects where the engineering firm specified ISO 2553 on the drawings but the fabrication shop (in a country using AWS) interpreted the symbols per AWS, welding the arrow side when the ISO symbol specified the other side.

Practical tip for international projects: When a fabrication drawing uses ISO symbols and the shop is in a country using AWS, always add a note in the general notes or tail of the first welding symbol: "Welding symbols per ISO 2553. Arrow-side weld indicated on solid reference line. Other-side weld indicated on dashed reference line." This one-line note has prevented rework costs exceeding $50,000 on large international fabrication packages.

Fillet size — leg length vs. throat thickness: AWS A2.4 specifies fillet size by leg length (the distance from the weld root to the weld toe along each leg). ISO 2553 can specify either throat thickness (a = the shortest distance from the weld root to the weld face, which equals 0.707 x leg length for an equal-leg fillet) or leg length (z). When an ISO drawing shows "a6" next to a fillet symbol, it means a 6 mm throat thickness, corresponding to an 8.5 mm leg length — NOT a 6 mm leg length. This difference alone has caused undersized fillet welds. Always verify whether a or z notation is used on ISO drawings.

Common Weld Symbol Mistakes and How to Avoid Them

Mistake 1 — Arrow pointed to the wrong member for a single-bevel groove weld. The arrow indicates which member is beveled. If the arrow points to the square-cut member, the bevel will be machined on the wrong plate and the joint will not fit up correctly. Verify: the arrow must point to the beveled member.

Mistake 2 — Forgetting to specify backing or backgouge for CJP groove welds welded from one side. A CJP groove weld welded from one side without backing or backgouge cannot guarantee complete penetration at the root. The root will contain slag, porosity, or incomplete fusion. Specify either a backing bar (rectangle with diagonal below reference line) or backgouging (note in tail: "Backgouge to sound metal, backweld").

Mistake 3 — Using identical fillet sizes on both sides without considering load direction. If the applied load puts one fillet in tension and the other in compression, one fillet carries most of the load. A 1/4-inch fillet on both sides may be inadequate if one side controls. Analyze the load path and size each fillet for its actual share of the load.

Mistake 4 — Omitting the field weld flag on welds that must be made after erection. A missing field weld flag defaults to shop weld. If a beam-to-column flange moment connection must be field-welded after erection, the flag is mandatory. Without it, the fabricator will weld the connection in the shop, and the beam cannot be erected.

Mistake 5 — Interpreting ISO 2553 symbols as AWS A2.4 without checking the drawing standard. Always check the general notes or title block for the governing welding symbol standard. If the standard is not stated, ask the engineer of record for clarification before releasing the drawing to the shop floor.

Mistake 6 — Specifying a concave contour on a fillet weld without considering the effective throat reduction. A concave fillet weld reduces the effective throat compared to a flat-faced fillet of the same leg size. The reduced throat must be verified to carry the design load. AISC 360 Table J2.5 (minimum fillet weld size) and the fillet weld strength calculation both assume a flat-faced fillet. A concave profile reduces the throat and therefore the capacity.

Frequently Asked Questions

What is the difference between a fillet weld and a groove weld?

A fillet weld joins two surfaces that are approximately perpendicular to each other — it is a triangular cross-section weld deposited in the corner of a T-joint, lap joint, or corner joint. A groove weld joins two members that are in the same plane (butt joint) — it fills a prepared groove (V, bevel, U, J) between the members. Fillet welds require no edge preparation (the connected members are cut square) but are less efficient in strength per unit of weld metal. Groove welds require machining or thermal cutting of a bevel, but a CJP groove weld develops the full tensile and flexural strength of the connected members.

When should I specify a CJP groove weld instead of fillet welds?

Specify a CJP groove weld when: (a) the connection must develop the full capacity of the connected member (e.g., moment connection beam flanges butt-welded to the column flange), (b) the connection is subject to cyclic or fatigue loading (fillet welds have a lower fatigue category than ground-flush CJP groove welds per AISC 360 Appendix 3), (c) the joint must have a flush surface (no projecting fillet that interferes with architectural finishes or equipment), or (d) the available length for fillet welds is insufficient to develop the required force. CJP welds cost roughly 3-5x more than fillet welds for the same force transfer — use fillet welds when they can do the job.

How do I read intermittent fillet weld symbols?

An intermittent fillet weld is shown with the weld length followed by a hyphen and the pitch (center-to-center spacing). For example, 3-12 means a 3-inch-long fillet weld segment repeated at 12-inch centers, leaving a 9-inch unwelded gap between segments. If the intermittent welds on the arrow side and other side are staggered (placed alternately along the joint), the fillet symbols are shown offset from each other (one shifted left, the other shifted right). If they are chain intermittent (aligned directly across from each other on opposite sides), the symbols are stacked symmetrically. Staggered intermittent welds are preferred over chain intermittent welds when heat input distortion is a concern — staggering distributes the heat input more evenly along the joint length.

Does the arrow side matter for a double-sided fillet weld with the same size on both sides?

No — if the fillet size, length, and pitch are identical on both sides, the arrow direction does not matter because the weld is symmetrical. The fabricator will place the same fillet on both sides regardless of which side the arrow points to. The arrow side convention matters only when: (a) the fillet welds are different sizes on each side (different leg dimensions), (b) the fillets are intermittent and staggered (the offset direction must be understood), (c) one side has a different contour or finish specification, or (d) for groove welds where the arrow indicates which member is beveled.

What does the circle symbol at the arrow-reference line junction mean?

The small circle at the junction of the arrow and the reference line means weld-all-around — the specified weld continues around the entire perimeter of the joint without interruption. This is most commonly used for HSS-to-base-plate connections (fillet weld all around the tube perimeter), pipe-to-flange connections (full-penetration groove weld all around the circumference), and gusset plate connections where the gusset is welded to the beam or column on all contact edges. The all-around symbol applies only to the joint that the arrow points to. It does not mean every weld on the drawing is all-around — each joint requires its own all-around symbol.

How do AWS A2.4 and ISO 2553 welding symbols differ?

The two standards differ in three critical areas: reference line layout, arrow-side convention, and fillet size notation. ISO 2553 uses a dual reference line — solid for the arrow side, dashed for the other side. AWS A2.4 uses a single reference line — below the line is arrow side, above is other side. ISO can specify fillet size by throat thickness (a) or leg length (z); AWS specifies by leg length only. ISO intermittent weld format uses number of segments, length, and pitch (n x l (e)); AWS uses length-pitch. These differences have caused fabrication errors on international projects when the shop interprets ISO symbols per the AWS convention and welds the wrong side of the joint. Always verify the governing standard before releasing drawings for fabrication.

What is the difference between CJP and PJP groove welds?

CJP (Complete Joint Penetration) groove welds have the weld metal fully penetrating through the entire joint thickness. The weld is as strong as the base metal in tension, flexure, and shear. PJP (Partial Joint Penetration) groove welds penetrate only part of the joint thickness. The effective throat of a PJP weld is the minimum distance from the weld face to the weld root. PJP welds are used where the full tensile strength of the connected member is not required, where a CJP weld would require impractical amounts of weld metal (very thick plates), or where access prevents welding from the second side. PJP welds are common in column base plates and heavy built-up sections where the load transfer does not require full penetration.

What information belongs in the tail of a welding symbol?

The tail (the V-shaped or forked opening at the end of the reference line opposite the arrow) carries supplementary information that does not fit in the symbol positions. Common tail contents: welding process (SMAW, FCAW-G, FCAW-S, GMAW, SAW, GTAW), filler metal specification (AWS classification, e.g., E70XX, E71T-1), welding position if restricted (flat only, horizontal only), preheat and interpass temperature requirements, post-weld heat treatment (PWHT) requirements, and any additional notes that cannot be communicated through the symbol alone. If the tail is empty (no text), no supplementary specification applies beyond the symbol.

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• EN 1993 connection design — Eurocode weld provisions
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Disclaimer — Educational Use Only

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer or welding engineer. Any weld symbol specifications, dimensions, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world welding symbol specifications depend on project-specific factors: joint configuration, base metal type and thickness, loading (static, cyclic, seismic), welding process, position, accessibility, governing code and project specification, and the qualified welding procedure specification (WPS). You are responsible for verifying all weld symbols against the governing drawing standard (AWS A2.4 or ISO 2553) and applicable design code, validating weld sizes and configurations with an independent method, and obtaining professional sign-off where required.

The site operator provides the content "as is" and "as available" without warranties of any kind. To the maximum extent permitted by law, the operator disclaims liability for any loss or damage arising from the use of, or reliance on, this page or any linked tools.