How to Read Weld Symbols — Step-by-Step
A welding symbol is read in a fixed sequence: (1) find the reference line, (2) identify arrow side vs. other side, (3) read the weld type symbol, (4) read size and length dimensions, (5) check for finishing codes or tail notes. Per AWS A2.4:2020.
The 5-Step Reading Method
Find the Reference Line
The reference line is always a horizontal line. Find it first. Everything else attaches to it — the arrow connects below or to one end; dimensions and weld symbols sit above or below it. The reference line is the anchor. Once you have it, the rest follows.
Identify Arrow Side vs. Other Side
The arrow points from the reference line to the actual joint on the drawing. The arrow side of the joint is where the arrow points. Any weld symbol placed below the reference line applies to the arrow side. Any symbol placed above the reference line applies to the other side — the opposite face of the joint. Both sides shown = weld both sides.
Identify the Weld Type
The weld symbol graphic tells you the weld type per AWS A2.4:2020:
Right triangle (vertical leg on left) = fillet weld — the most common weld in structural steel.
Open-V = V-groove weld. Open-V with one straight side = bevel groove. Square groove = two parallel lines from the reference line.
Circle on reference line = plug or slot weld (filled circle = plug; elongated shape = slot).
Two half-circles = seam weld. No symbol with broken arrow = bevel or J-groove on the arrow member.
Read the Dimensions
Left of the weld symbol = weld size. For fillet welds, this is the leg length. For groove welds, the depth appears in parentheses — e.g., (5/8) means 5/8-inch groove depth.
Right of the weld symbol = length and pitch for intermittent welds. Written as length-pitch: 3-12 means 3-inch welds placed 12 inches center-to-center. No number to the right = the weld is continuous.
No size on a groove weld = CJP (complete joint penetration). The joint must be fully fused through its entire thickness.
Check for Special Indicators
Solid triangle flag at junction = field weld. The weld must be made at the erection site, not in the shop.
Circle at junction = weld-all-around. The weld must be made continuously around the full joint perimeter.
Tail (V-shape at the reference line end opposite the arrow) = WPS reference number, process designation (SMAW, FCAW, GMAW), or special instruction. No tail = no special note required.
Contour and finish symbols = a letter on or near the weld symbol (C = chipping, G = grinding, M = machining, U = unspecified) with a straight or convex/concave contour line indicates a finishing requirement after welding.
Reading a Real Fillet Weld Symbol
Take a welding symbol showing: a right triangle below the reference line with the number 3/8 to its left and 3-12 to its right. Here is the full reading:
Step 1 — Reference line: Found. Horizontal line with arrow and triangle.
Step 2 — Arrow side: Triangle is below the reference line = arrow side weld.
Step 3 — Weld type: Right triangle with vertical leg on left = fillet weld.
Step 4 — Dimensions: 3/8 to the left = 3/8-inch fillet leg size. 3-12 to the right = 3-inch weld segments, 12-inch center-to-center pitch (intermittent fillet weld).
Step 5 — Special indicators: No flag, no circle, no tail. Standard shop weld, no special finishing required.
Full reading: Make 3/8-inch fillet welds on the arrow side of the joint. Each weld segment is 3 inches long, spaced 12 inches center-to-center along the joint.