Welding Symbols Chart: How to Read Blueprints

Welding symbols on blueprints are a compact language for telling a welder what joint to weld, where the weld goes, how large it must be, and what extra requirements apply. Once you understand the reference line, arrow, weld symbol, dimensions, and supplementary marks, most drawings become much easier to read. The key is to decode each part in a consistent order rather than trying to interpret the whole symbol at once.

Last checked: September 28, 2026. Dates and figures were verified against official sources.

Key Takeaways

What Are Welding Blueprint Symbols?

Welding blueprint symbols are standardized marks that communicate weld type, location, dimensions, contour, and other fabrication requirements. In U.S. practice, the primary reference is AWS A2.4:2020, Standard Symbols for Welding, Brazing, and Nondestructive Examination.

It helps to distinguish two related terms. A weld symbol is the small geometric mark that identifies a weld type, such as the triangle used for a fillet weld. A welding symbol is the complete instruction made from the reference line, arrow, weld symbols, dimensions, supplementary marks, and optional tail.

The system lets a designer place a large amount of fabrication information on a drawing without writing a paragraph beside every joint. The welder can identify the joint, determine which side is involved, read the required weld geometry, and then check any notes or procedure references.

Common drawings use symbols for fillet welds, several groove preparations, plug and slot welds, spot and seam welds, edge welds, backing, studs, and surfacing. Not every welding symbol contains every possible element.

How Welding Symbols Are Built

A welding symbol is built around a horizontal reference line and an arrow that points to the joint or area being specified. The weld symbol and dimensions are arranged around that line according to standardized positions.

The main parts are:

• Arrow: points to the joint, location, or member involved.
• Reference line: carries the weld symbols, dimensions, and supplementary information.
• Weld symbol: identifies the required weld form, such as fillet, V-groove, plug, or spot.
• Dimensions: communicate values such as weld size, groove depth, length, pitch, root opening, or groove angle when applicable.
• Supplementary symbols: add requirements such as field welding, weld-all-around, contour, backing, or melt-through.
• Tail: provides a place for a process, specification, WPS, or another reference when one is needed.

The tail is not mandatory on every symbol. If no additional reference is required, AWS permits it to be omitted.

One detail matters more than it first appears: information below and above the reference line is not interchangeable. AWS guidance confirms that information for the arrow side is placed below the reference line. AWS discusses this arrow-side convention because misreading it can put the weld on the wrong face of the joint.

Common Joint Types and Symbol Basics

Joint type describes how the pieces of base metal meet; the weld symbol describes the weld required at that joint. These are related concepts, but they are not the same thing.

The five basic joint configurations commonly used in welding drawings are butt, corner, T, lap, and edge joints.

Common Joint Types

Each basic joint arrangement creates different access, load-transfer, and preparation conditions. The drawing may therefore use different weld symbols on the same general joint type depending on the design.

• Butt joint: two members meet edge to edge in roughly the same plane.
• Corner joint: two members meet to form a corner.
• T-joint: one member meets another at an angle that forms a T-shaped arrangement.
• Lap joint: one member overlaps another.
• Edge joint: adjacent edges are positioned next to each other and joined along the edge.

Fillet welds commonly appear on T, lap, and corner joints. Groove welds are common on butt joints but may also be used in other configurations when the joint is prepared for penetration.

Basic Symbol Elements

The geometric mark tells you the weld form, while its position and nearby dimensions tell you how that weld is to be made. The chart below summarizes common AWS-style symbols in plain language.

Drawings made to another standard may arrange information differently. ISO 2553:2019 recognizes more than one symbolic system, so you should establish the governing standard before interpreting an unfamiliar or imported drawing.

Fillet and Groove Weld Symbols

Fillet and groove symbols describe two of the most common weld families found on fabrication drawings. A fillet symbol identifies a weld placed in a corner, while a groove symbol also communicates how the joint edges are prepared.

The fillet weld symbol is a right triangle. The perpendicular leg of the symbol is drawn on the left, and the required fillet size is placed to the left of the symbol.

If unequal fillet legs are required, both leg dimensions may be given. The drawing must make clear which dimension applies to which leg.

Groove symbols include square, V, bevel, U, J, flare-V, and flare-bevel forms. Depending on the groove, the symbol may also carry the groove weld size, depth of preparation, root opening, groove angle, and other joint details.

A bevel groove or J-groove prepares only one joint member. When the prepared member is not otherwise obvious, a break in the arrow can identify which member receives that preparation.

Do not assume every groove symbol means complete joint penetration. Read the dimensions, tail, applicable detail, and governing welding requirements together.

Plug, Slot, Spot, and Seam Welds

Plug, slot, spot, and seam symbols are commonly used where members overlap or where the joint is made at discrete points or along a line. Their dimensions and side significance differ from ordinary fillet-weld notation, so they should be read as their own symbol families.

A plug weld is made through a generally round hole in one overlapping member. Weld metal fills the opening and fuses with the member beneath.

A slot weld follows the same basic idea but uses an elongated opening. The symbol can communicate slot width, length, pitch, number of slots, and filling depth where required.

Spot welds use a circle as the basic weld symbol. Seam welds use a circle crossed by parallel horizontal lines. The welding process may need to be identified separately because the basic geometry alone does not necessarily tell you how the spot or seam is produced.

The Miller guide to weld symbols also shows how plug, slot, fillet, and groove dimensions are arranged around their symbols.

How to Read Weld Size, Length, and Pitch

Weld dimensions are read by position around the weld symbol. For common fillet notation, the weld size goes to the left, while weld length and intermittent-weld pitch go to the right.

1. Identify the weld type. A number can mean different things for different symbols, so first determine whether you are reading a fillet, groove, plug, slot, spot, seam, or another weld.
2. Read the value to the left. On a fillet weld, this normally specifies the leg size. On other weld types, the meaning follows that symbol’s dimensional rules.
3. Read the value to the right. A single value commonly identifies the weld length where length must be specified.
4. Look for length-pitch notation. On an intermittent weld, two values separated by a dash show weld-segment length first and pitch second.
5. Remember what pitch means. Pitch is the center-to-center spacing between repeated weld segments, not simply the open gap between them.
6. Check the drawing units. Dimensions must be interpreted using the units and conventions governing that drawing.

For example, a fillet symbol with a size of 1/4 to the left and 2-6 to the right describes a 1/4-inch fillet with 2-inch weld segments at a 6-inch center-to-center pitch when the drawing uses inches.

There is no universal “1/16th rule” that converts welding-symbol dimensions. Fractions such as 1/16 inch may appear on individual drawings, but you should read the actual dimensions and declared drawing units rather than apply a general conversion rule.

Contour and Finish Symbol Marks

Contour symbols tell you the required final profile of the weld face. AWS notation includes flush or flat, convex, and concave contours, which may be achieved by welding or by an indicated finishing operation.

If a specific mechanical finishing method is required, a letter can be placed with the contour symbol. AWS A2.4:2020 uses the following designators:

• C: chipping
• G: grinding
• H: hammering
• M: machining
• P: planishing
• R: rolling
• U: unspecified mechanical finishing method

The finish letter tells the fabricator how the requested contour is to be produced. It does not by itself specify a surface-roughness value or weld-quality acceptance level.

Keep contour information separate from groove dimensions. A groove angle or root opening defines joint geometry, while a contour mark describes the required profile at the finished weld face.

Arrows, Sides, and Field Welds

The arrow connects the welding instruction to a specific joint, location, or member. The placement of the weld symbol above or below the reference line then tells you which side of that joint the instruction applies to under AWS notation.

A small flag at the junction of the arrow and reference line indicates a field weld, meaning the weld is to be made at the field or erection location rather than as an ordinary shop weld.

Arrow Direction And Joint Location

Start by following the arrow to the joint rather than judging the weld side from the arrow’s visual direction on the page. The arrow may point upward, downward, left, or right without changing the basic AWS above/below rule.

The physical side of the joint touched by the arrow is the arrow side. The opposite face is the other side.

For asymmetric groove preparations such as certain bevel- and J-groove joints, the arrow may contain a break that identifies the member to be prepared. That detail is different from the arrow-side/other-side rule and should be read separately.

• Follow the arrow to the joint.
• Identify which physical face is the arrow side.
• Check whether the arrow has a break identifying a prepared member.
• Then read the weld symbol’s position above or below the reference line.

Side Placement And Field Welds

Under AWS A2.4, a weld symbol below the reference line applies to the arrow side. A weld symbol above the line applies to the other side.

If appropriate weld symbols appear both above and below the line, welding is being specified on both sides. The exact weld type and dimensions must still be read independently for each side.

A field-weld flag is placed at the junction of the arrow and reference line. A weld-all-around symbol is a circle at that junction and indicates that the specified weld continues around the joint as applicable.

Do not confuse the weld-all-around circle with the circular basic symbol used for a spot or projection weld. Their positions within the complete welding symbol are different.

Tails, Notes, and WPS Callouts

The tail is the forked part at the end of the reference line opposite the arrow. It carries information that does not fit into the normal geometric and dimensional positions of the welding symbol.

A tail may identify a welding process, specification, procedure, WPS, or another reference needed to execute the joint correctly. When there is no reference to include, AWS allows the tail to be omitted.

A Welding Procedure Specification (WPS) contains the controlled welding variables and instructions required by the applicable procedure. A drawing can reference a WPS in the tail rather than attempting to place all procedure details on the welding symbol.

• Read the weld geometry from the basic symbol and its dimensions.
• Read field, all-around, contour, and other supplementary requirements separately.
• Use the tail for process or document references.
• Check drawing notes when the symbol refers to information located elsewhere.

A welding symbol defines the drawing requirement; a referenced WPS supplies the procedure details needed to make the weld under the applicable rules.

Practice Reading Welding Blueprint Symbols on Drawings

The easiest way to read welding blueprint symbols consistently is to use the same sequence every time. This prevents you from noticing a familiar triangle or V-shape and overlooking a side, length, contour, or field-weld requirement.

1. Find the arrow. Identify the exact joint or area the symbol addresses.
2. Determine the side. Under AWS notation, below the reference line means arrow side and above means other side.
3. Name the weld symbol. Decide whether it is a fillet, groove, plug, slot, spot, seam, edge, or another weld form.
4. Read the left-side dimensions. Determine the specified size, groove depth, or other value appropriate to that weld type.
5. Read the right-side dimensions. Check weld length, pitch, or other applicable spacing information.
6. Look for supplementary symbols. Check for field weld, weld-all-around, backing, melt-through, contour, or finish requirements.
7. Read the tail and notes. Follow any process, WPS, specification, or detail reference.
8. Confirm the governing standard and drawing units. Do this before acting on a symbol that is unfamiliar or appears inconsistent.

As a simple example, imagine an AWS fillet symbol below the reference line with 1/4 on its left and 2-6 on its right. Read it as an arrow-side fillet weld, 1/4 inch in size, made in 2-inch segments on 6-inch centers when the drawing is dimensioned in inches.

If a flag also appears at the arrow/reference-line junction, that same weld is a field weld. If a grinding finish letter and contour mark are added, those requirements become part of the instruction as well.

Frequently Asked Questions

How Do You Read Blueprints for Beginners?

Beginners should first identify the title block, drawing views, dimensions, notes, scale, and revision information. For welding drawings, then locate each arrow and reference line, identify the weld symbol, read its dimensions, and check supplementary marks and notes before interpreting the joint.

How to Show Welding Symbols on Drawings?

Welding symbols are shown with an arrow pointing to the joint and a reference line carrying the weld symbol and required dimensions. Supplementary symbols can add field-weld, all-around, contour, backing, or other requirements, while an optional tail can reference a process, WPS, specification, or detail.

How to Read a Welding Plan?

Read a welding plan by identifying the drawing standard and units first, then follow each welding-symbol arrow to its joint. Decode the side, weld type, dimensions, supplementary symbols, tail references, and drawing notes before comparing the requirement with the applicable WPS or fabrication documents.

How to Read Welding Blueprints Pdf?

A welding blueprints PDF is read the same way as a printed fabrication drawing. Zoom in enough to see the arrow, reference line, weld symbol, dimensions, supplementary marks, tail, and notes, then confirm the title block, revision, units, and governing symbol standard before using the information.

What Does Above or Below the Reference Line Mean?

Under AWS A2.4, a weld symbol below the reference line applies to the arrow side of the joint, while a symbol above the line applies to the other side. Symbols shown on both sides of the line specify welding on both sides as indicated.

What Do the Circle and Flag Mean on a Welding Symbol?

A circle at the junction of the arrow and reference line is the weld-all-around symbol, while a flag at that junction indicates a field weld. These are supplementary symbols and should not be confused with basic weld symbols such as the circle used for a spot weld.

Conclusion

Welding symbols become much easier to read when you decode them in order: joint, side, weld type, dimensions, supplementary marks, then tail and notes. Before fabrication, confirm the governing symbol standard, drawing units, revision, and any referenced WPS so the marks on the blueprint translate into the weld the designer actually specified.

Sources

1. American Welding Society — AWS A2.4:2020: Current AWS standard for welding, brazing, and nondestructive examination symbols.
2. American Welding Society — Welding Symbol Guidance: Arrow-side and other-side interpretation under AWS A2.4.
3. Miller — How to Read and Understand Weld Symbols: Practical examples of fillet, groove, plug, slot, size, length, pitch, and supplementary symbols.
4. ISO 2553:2019: International symbolic representation systems for welded joints on technical drawings.