To read a welding symbol, start at the arrow to find the joint, then check whether the weld symbol sits below the reference line (arrow side) or above it (other side), name the weld type, and read the size on the left and the length and pitch on the right. These conventions come from AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination, the standard behind the symbols questions on CWI Part A.
To look up a single symbol, such as a flare-bevel, a spacer or an NDE letter, use our welding symbols chart, which lists every weld, supplementary and NDE symbol in tables with labelled drawings.
Where each piece of information goes
| Position on the symbol | What it tells you |
|---|---|
| Below the reference line | Weld on the arrow side of the joint |
| Above the reference line | Weld on the other side |
| Left of the weld symbol | Fillet size, or groove depth with the weld size in parentheses |
| Right of the weld symbol | Length, then pitch after a hyphen |
| Inside a groove symbol | Root opening |
| Outside a groove symbol | Groove angle |
| Where the arrow meets the line | Flag for field weld, circle for weld all around |
| Next to the weld symbol, away from the line | Contour, with a finishing letter |
| Tail | Process, specification or WPS reference |
The reference line is always drawn horizontal. The tail never tells you a side, and the rules don't change when the arrow points left instead of right.
Read every symbol in the same order
- Find the joint. Follow the arrow. The side of the joint it touches is the arrow side.
- Check the side. Below the line is the arrow side, above is the other side, and both means weld both sides.
- Name the weld. Triangle for fillet; groove shapes for square, V, bevel, U and J; rectangle for plug or slot.
- Read the left. Fillet size, or groove depth and weld size.
- Read the right. Length and pitch. No length means the weld runs the full length of the joint.
- Read groove details. Root opening inside the symbol, groove angle outside it.
- Check the arrow end and around the weld symbol. Field weld flag, weld-all-around circle, melt-through, backing, contour and finish.
- Read the tail and any extra reference lines. With more than one reference line, the line nearest the arrow is done first.
Using the same order every time keeps you from skipping the side check.
Worked example 1: intermittent fillets on both sides
A T-joint. The arrow touches the left face of the upright plate. A fillet symbol sits below the line with 5/16 on its left and 3-8 on its right. A second fillet symbol sits above the line, shifted along so it does not line up with the one below, with the same numbers.
- Side: symbols above and below, so welds on both sides.
- Weld: fillet.
- Size: 5/16 in. on each side.
- Length and pitch: welds 3 in. long, spaced 8 in. center to center. Pitch is measured center to center, from the middle of one weld to the middle of the next.
- Pattern: because the two symbols are offset, the welds are staggered. If they lined up directly opposite each other, they would be chain intermittent welds.
Worked example 2: a bevel groove with a broken arrow
A butt joint. The arrow has a break in it and points to the right-hand plate. A bevel groove symbol sits below the line. To its left is 3/8 (1/2). Inside the symbol is 1/8. Outside it, away from the line, is 45°.
- Side: below the line, so the arrow side.
- Which plate is beveled: the broken arrow points to the member that gets the preparation, so the right-hand plate.
- Depth and size: 3/8 in. depth of bevel, and 1/2 in. groove weld size in parentheses.
- Root opening: 1/8 in.
- Groove angle: 45°.
The weld size is larger than the bevel depth here, which means the weld is expected to penetrate past the prepared depth.
Worked example 3: a V-groove with no size
A V-groove symbol sits below the line with no number to its left and a root opening of 0 inside. Above the line, opposite the groove, is a filled semicircle.
- Side: the groove weld is on the arrow side.
- Size: for a single groove, no depth or size means complete joint penetration.
- Root opening: zero.
- Filled semicircle: the melt-through symbol. It calls for visible root reinforcement on the other side of a joint welded from one side.
Worked example 4: a field weld all around, with a tail
A pipe column meets a base plate. A fillet symbol sits below the line with 1/4 on its left and nothing on its right. At the junction of the arrow and the line are a circle and a flag. The tail reads WPS 12.
- Side and weld: a 1/4 in. fillet on the arrow side.
- Length: none given, and the circle means weld all around, so the fillet goes the whole way around the joint.
- Flag: field weld, made on site rather than in the shop.
- Tail: weld to WPS 12.
Read in one line: a 1/4 in. fillet all around the column, made in the field, to WPS 12.
Mistakes to watch for
- Treating pitch as the gap between welds. It is center to center.
- Reading the side from the tail or the arrow direction. Only above or below the line sets the side.
- Mixing up the backing and plug symbols. Both are rectangles. Backing sits opposite a groove symbol; a plug or slot weld symbol is the weld itself.
- Missing the parentheses. Groove depth and groove weld size are different numbers.
- Assuming a drawing uses AWS rules. ISO 2553 shows the other side differently, with a dashed line. Check which standard the drawing follows.
Symbols on the CWI exam
Symbols are one of the larger topics on CWI Part A, which is closed book, so these rules need to be memorized. Keep the welding symbols chart open while you practice, and use the symbols study guide for the reasoning behind each rule.
Test yourself with the free symbols practice questions, or take the free CWI Part A diagnostic to see how symbols compare with your other topics.
Frequently asked questions
How do you read a welding symbol?
Start at the arrow to find the joint, then check whether the weld symbol is below the reference line (arrow side) or above it (other side). Name the weld type, read the size to the left and the length and pitch to the right, then check the arrow end, the groove details and the tail.
What is the arrow side on a welding symbol?
The arrow side is the side of the joint the arrow touches. A weld symbol drawn below the reference line puts the weld on the arrow side. A symbol above the line puts it on the other side.
What do the numbers on a welding symbol mean?
Numbers to the left of the weld symbol give the size, such as fillet leg size or groove depth. Numbers to the right give the length and then the pitch, joined by a hyphen. For grooves, a number inside the symbol is the root opening and an angle outside it is the groove angle.
What does a broken arrow mean on a welding symbol?
A broken arrow points to the member that gets the edge preparation in a bevel or J-groove weld. The break can be left off when it is obvious which member is prepared.
What does a welding symbol with no length mean?
No length means the weld runs the full length of the joint. To carry a weld around corners, the symbol needs the weld-all-around circle or separate symbols for each side.
Are AWS and ISO welding symbols the same?
No. AWS A2.4 uses the position above or below a single reference line to show the side. ISO 2553 adds a dashed line to show the other side. Check which standard a drawing uses before you read it.
Sources
Our Symbols: Welding and NDE questions cite these documents, by document and, where we can confirm it, chapter or section.
- AWS A2.4 (28 questions)
We are not affiliated with AWS and never see real exam questions. Every question is written from AWS's public content outline and the standards it names, so nothing here is a leaked or recalled item. How we write questions
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