WELDING REFERENCE
Weld Symbol Chart — AWS A2.4 & ISO 2553
Complete reference for all AWS A2.4 weld symbols with ISO 2553 equivalents. Covers arrow‑side rules, dimension notation, supplementary marks, and common mistakes. Includes a free Excel download.
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All AWS A2.4 & ISO 2553 symbols
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Arrow‑side & dimension rules
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Free Excel & PDF downloads
Weld Symbol Chart
Quick reference at a glance
FilletTriangle — most common
GrooveV, U, J, bevel, square
Plug / SlotRectangle with dimensions
SupplementaryAll-around, field weld, contour
Reference Chart
AWS A2.4:2020 & ISO 2553:2019
WELDING SYMBOLS
What Is a Weld Symbol Chart?
A weld symbol chart is the engineer’s quick‑reference for decoding welding callouts on fabrication drawings. It shows each symbol, its arrow‑side placement, size notation, and supplementary marks — all organized for fast lookup.
A fabrication drawing lands on your desk. It has a reference line, an arrow, a triangle, and a flag — plus numbers scattered on either side of a symbol you half‑remember from your college drafting course. You need to know exactly what that symbol means, because if you misinterpret it, a $5,000 weldment turns into scrap. This chart gives you the answer in seconds — what each symbol looks like, which side of the joint it applies to, how dimensions are placed, and what those supplementary marks mean for the finished weld.
Arrow‑Side Rule
Symbols below the reference line = weld the side the arrow points to. Symbols above = weld the opposite side. Misreading this rule causes more rework than any other drafting error.
Dimensions & Notation
Size is always on the left of the symbol. Length and pitch go to the right (e.g., 50‑150). Groove welds use D(S) format — depth and effective throat.
Supplementary Marks
Weld‑all‑around, field weld flag, melt‑through, contour and finish symbols — each small mark changes where and how the weld is performed. Don’t miss them.
WELD SYMBOL REFERENCE
Weld Symbol Chart — Quick‑Reference Table
Complete AWS A2.4:2020 weld symbols with ISO 2553 equivalents. Covers fillet, groove, plug, slot, spot, seam, stud, surfacing, edge, and backing welds — plus all supplementary marks.
Note: Symbols are shown in their standard AWS A2.4 orientation. For ISO 2553 System A, the arrow‑side and other‑side conventions differ (see the AWS vs. ISO section below). Always verify the governing standard from the drawing title block before interpreting any symbol.
Fillet & Groove Weld Symbols
Arrow‑side = symbol below the reference line; other‑side = above. Size to the left, length‑pitch to the right. Groove welds use D(S) notation: depth of preparation (weld size).
| Weld Type | Symbol Shape | Arrow‑Side (Below Line) | Other‑Side (Above Line) | Size Notation | Typical Application |
|---|---|---|---|---|---|
| Fillet | Right triangle | Triangle below | Triangle above | Leg size left (e.g., `6` = 6mm leg) | T‑joints, lap joints — the most common weld |
| Square Groove | Two parallel vertical lines | Square below | Square above | Weld size in parentheses | Butt joints on thin material — no edge prep |
| V‑Groove | V shape | V below | V above | D(S) — depth D, weld size S in parentheses | Butt joints — both edges beveled to a V |
| Bevel Groove | Single angled line | Bevel below | Bevel above | D(S) — depth of bevel, weld size | Butt joints — only one plate edge prepared |
| U‑Groove | U shape | U below | U above | D(S) — depth of U‑prep, weld size | Thick‑plate butt joints — less filler than V |
| J‑Groove | J shape | J below | J above | D(S) — depth of J‑prep, weld size | Thick‑plate butt — single‑sided curved prep |
| Flare‑V | Flared V shape | Flare‑V below | Flare‑V above | Weld size in parentheses | Two round or curved members — tubular structures |
| Flare‑Bevel | Flared bevel | Flare‑bevel below | Flare‑bevel above | Weld size in parentheses | Round member meeting a flat member — tube‑to‑plate |
Special Weld & Supplementary Symbols
Plug, slot, spot, seam, stud, surfacing, edge, backing, and melt‑through. Supplementary marks (weld‑all‑around, field weld, contour) modify the base symbol.
| Symbol Type | Symbol Shape | Arrow‑Side | Other‑Side | Size / Notation | Meaning / Application |
|---|---|---|---|---|---|
| Plug Weld | Rectangle | Rectangle below | Rectangle above | Hole diameter left, depth inside, pitch right | Lap joints — fill drilled/punched hole |
| Slot Weld | Elongated rectangle | Slot below | Slot above | Width left, length‑pitch right, depth inside | Wider lap joints — elongated hole |
| Spot Weld | Circle | Circle below | Circle above | Diameter left, pitch right, count in parentheses | Resistance welding — sheet metal assemblies |
| Seam Weld | Circle with horizontal line | Seam below | Seam above | Width left, length‑pitch right | Continuous resistance seam — leak‑tight joints |
| Stud Weld | Circle on cross | Stud below | (Not used) | Size left, pitch right | Shear connectors, threaded studs |
| Surfacing | Horizontal bar with arrow | Surfacing below | (Not used) | Deposit height left | Hard‑facing, wear‑resistant overlay |
| Back / Backing | Rectangle | Backing below weld symbol | Backing above | (Process in tail) “R” = removable | Backing bar for root pass support |
| Edge Weld | Angled lines at edges | Edge below | Edge above | Size (deposit height) left | Edge joints — thin sheet flanges |
| Weld‑All‑Around | Hollow circle | At junction of arrow & line | — | — | Weld extends around entire perimeter |
| Field Weld | Filled flag | At junction, pointing toward symbol | — | — | Weld performed on‑site during erection |
| Melt‑Through | Filled semicircle | Opposite side of groove symbol | — | — | Complete joint penetration from one side |
| Contour (Flat) | Straight line | Above or below symbol | — | Finish method letter (G, M, C, H) | Weld face ground/machined flush |
| Contour (Convex) | Curved outward | Above or below | — | Finish method letter | As‑welded crown above base metal |
| Contour (Concave) | Curved inward | Above or below | — | Finish method letter | Dished below surface — reduces stress concentration |
Download Free Resources
Excel Spreadsheet (.xlsx): Filterable, sortable table with AWS section references and ISO 2553 equivalents. Download Excel →
PDF Desk Reference (Letter/A4): Single‑page quick lookup. Download PDF →
Shop Floor Poster (Tabloid/A3): Wall‑mount, large‑format symbols. Download Poster →
Governing Standards
Data compiled from AWS A2.4:2020 and ISO 2553:2019. Always verify the governing standard from the drawing title block. For critical applications, consult a Certified Welding Inspector (CWI).
READING GUIDE
How to Read a Welding Symbol — Step by Step
Follow these eight steps to decode any welding symbol on a fabrication drawing. Work through them in order — each step builds on the last, and skipping one is how costly mistakes slip through.
01
Find the Reference Line
This horizontal line anchors everything. If there are multiple reference lines, start with the one closest to the arrow — it represents the first operation.
02
Follow the Arrow to the Joint
The arrow points to exactly where the weld goes. For bevel and J‑grooves, a broken arrow indicates which side receives the edge preparation.
03
Determine Arrow‑Side vs. Other‑Side
Symbols below the line = arrow side. Symbols above = other side. Both sides = weld both faces. Confirm the governing standard (AWS or ISO) from the title block.
04
Identify the Weld Type from the Symbol Body
Triangle = fillet. V = V‑groove. Rectangle = plug or slot. Circle = spot. Circle with line = seam. U = U‑groove. J = J‑groove.
05
Read the Dimensions
Size is always on the left. Length and pitch on the right in length–pitch format (e.g., 50‑150). Groove welds use D(S) = groove depth (weld size).
06
Check Supplementary Symbols
Look for weld‑all‑around circle, field weld flag, melt‑through semicircle, contour symbols, and finish method letters (G, M, C, H).
07
Read the Tail
The tail may specify process (GMAW, GTAW, SMAW, FCAW, SAW), WPS number, filler metal, or NDE requirements (RT, UT, MT, PT). Don’t skip it.
08
Confirm the Governing Standard
Check the drawing’s title block. AWS A2.4 and ISO 2553 use different arrow‑side conventions. If not stated, ask the design authority before welding.
Example: Interpreting a Fillet Weld Callout
You see a reference line with a triangle below it, the number `6` to the left, and `50-150` to the right. There is no tail. This means: a 6mm equal‑leg fillet weld on the arrow side, with 50mm weld segments spaced 150mm center‑to‑center (intermittent). If the triangle were above the line, the weld would go on the other side. If there were a flag at the junction, it would be a field weld. If a circle were at the junction, it would be weld‑all‑around. This simple example shows how each element contributes to the complete instruction.
6Leg size (left)
50‑150Length‑pitch (right)
Triangle belowArrow‑side fillet
Welding Symbol Anatomy — The 8 Elements
A weld symbol is one piece of a larger puzzle. The welding symbol — the complete assembly on a drawing — consists of up to eight standardized elements. Understanding how they fit together is what separates reading a drawing correctly from guessing.
| Element | What It Looks Like | What It Specifies |
|---|---|---|
| Reference Line | Horizontal line (backbone of the symbol) | All other elements are placed on or around this line. Must always be drawn horizontally. |
| Arrow | Line connecting reference line to the joint | Points to the joint requiring welding. For bevel/J‑grooves, a broken arrow indicates which member receives edge preparation. |
| Weld Symbol Body | Triangle, V, U, J, rectangle, circle, etc. | Indicates the type of weld required — fillet, groove, plug, spot, seam, etc. |
| Size (Left of Symbol) | Number(s) to the left | For fillets: leg length. For grooves: effective throat or D(S) notation. Always placed left of the symbol. |
| Length‑Pitch (Right of Symbol) | e.g., 50‑150 or just a length | Length of intermittent weld segments and center‑to‑center spacing. If no dash, weld is continuous. |
| Supplementary Marks | Circle, flag, semicircle, contour lines, letters | Weld‑all‑around, field weld, melt‑through, contour (flat/convex/concave), finish method (G, M, C, H). |
| Tail (Optional) | Forked extension at the end of reference line | Holds process specification (SMAW, GMAW, GTAW, etc.), WPS number, filler metal, or NDE requirements. |
| Multiple Reference Lines | Additional solid lines below the main line | Indicates a sequence of operations — the line nearest the arrow is performed first. |
Design tip: The most critical rule to memorize is the arrow‑side / other‑side placement. In AWS A2.4, symbols below the line = arrow side; above = other side. In ISO 2553 System A, the arrow side is shown on a solid line and the other side on a dashed identification line. Always verify which standard governs your drawing.
AWS vs. ISO & COMMON MISTAKES
AWS A2.4 vs. ISO 2553 — Key Differences & Costly Errors
Engineers working across international supply chains encounter two dominant standards. Understanding the differences — and the five most common symbol mistakes — can save weeks of rework.
The symbols themselves are largely the same, but the conventions for placing them differ — and this is where costly misinterpretation happens. Below we compare the two systems, then highlight the top five errors we catch during DFM review.
AWS A2.4 (North America)
Arrow‑Side = Below the Line
Symbol placed below the solid reference line indicates arrow side. Symbol above = other side. Both sides = symbols on both sides. Used in USA, Canada, Mexico, Japan (JIS‑aligned). Tail common for process and WPS.
ISO 2553 System A (Europe)
Solid vs. Dashed Identification Lines
Symbol on the solid line = arrow side (near side). Symbol on the dashed line = other side (far side). Used in EU, UK, Australia (AS 1101.3), India. Tail less common; specifications often elsewhere on the drawing.
Dimension Placement
Different Conventions
AWS places size left and length‑pitch right of the symbol. ISO often places dimensions above or below the reference line, following a different convention. Always verify the standard.
5 Common Weld Symbol Mistakes That Add Cost
During DFM review at our Qingdao facility, our engineers review thousands of fabrication drawings each year. These five errors appear most frequently — and they’re all avoidable with a careful check against this chart.
- 1. Arrow‑Side / Other‑Side Reversal: Welding the wrong side. Always confirm the standard (AWS vs. ISO) from the title block.
- 2. Missing Weld Size: No dimension forces the fabricator to guess — leading to over‑welding and extra cost. Every symbol should carry a size.
- 3. Missing Field Weld Flag: A flag omitted means shop welding; but if the assembly is erected on‑site, missing it causes the weld to be made in the wrong location.
- 4. Confusing Weld‑All‑Around with Spot Weld: Both are circles — but the all‑around symbol is at the junction, while the spot symbol is on the reference line. Different meanings, different outcomes.
- 5. Non‑Standard or Improvised Symbols: Hand‑drawn marks or margin notes place the interpretation burden on the fabricator. Stick to AWS or ISO symbols; if something isn’t covered, put it in the tail as a written spec.
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Frequently Asked Questions
Weld Symbol Chart FAQs
A weld symbol is the individual pictograph — the triangle for a fillet, the V for a V-groove, the rectangle for a plug — indicating the type of weld. A welding symbol is the complete assembly: the reference line, arrow, weld symbol, dimensions, supplementary symbols, contour and finish specifications, and tail. The weld symbol is one ingredient; the welding symbol is the entire recipe for producing the joint.
A hollow circle placed at the junction of the arrow and reference line means the weld must extend continuously around the entire perimeter of the joint. It is commonly used on tube-to-plate connections, pipe-to-flange joints, and structural hollow sections. Do not confuse this with a spot weld symbol — a circle placed on the reference line itself, not at the junction.
The filled triangular flag — called the field weld symbol — placed at the junction of the arrow and reference line means the weld is to be performed on-site during erection or installation, not in the fabrication shop. If the flag is absent, the default assumption is shop welding.
Both standards use the same basic weld symbol pictographs, but they differ in how arrow-side and other-side are indicated. AWS A2.4 (North America) places the weld symbol below a single solid reference line for the arrow side and above it for the other side. ISO 2553 System A (Europe) uses a solid reference line for the arrow side and a dashed identification line for the other side. Always verify which standard governs from the drawing title block.
CJP (Complete Joint Penetration) means the weld metal extends through the full thickness of the joint with fusion at the root. It is specified in one of three ways: (1) placing “CJP” in the tail, (2) omitting depth-of-bevel and weld-size dimensions from the groove weld symbol, or (3) adding a melt-through or back-weld symbol on the opposite side of the reference line.
Yes. A printable PDF desk reference (letter/A4) and a shop-floor poster format (tabloid/A3) are both available for free download. An Excel spreadsheet version with filterable, sortable columns and ISO 2553 equivalents is also available — it’s the only weld symbol chart in .xlsx format on the web.
Get Your Parts Made Right — Free DFM Review with Every Quote
You’ve looked up the symbol. You’ve verified the arrow side, checked the dimensions, and confirmed the standard. Now you need someone to manufacture the parts on that drawing — accurately, on time, and at a fair price. At Baetro, every quote includes a free DFM review. Our engineers check your drawings for the exact symbol errors documented on this page — plus tolerance stack‑ups, material selection, and manufacturability optimizations that often reduce cost by 20% or more.
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