Engineering drawings use standardized symbols to communicate information about materials, welds, surface finishes, dimensions, and structural elements. This reference covers the most commonly used symbols in civil and structural engineering drawings, organized by category.

Structural steel symbols

Structural steel sections are identified by letter codes on drawings. These codes indicate the section type and are followed by dimensions or a designation number.

W — Wide flange beam (I-beam), e.g. W12×26 (12 inch nominal depth, 26 lb/ft)
S — American Standard beam
C — Channel section
L — Angle (equal or unequal leg), e.g. L4×4×½
HSS — Hollow Structural Section (square, rectangular, or round tube)
PL — Plate, e.g. PL½×8 (½ inch thick, 8 inches wide)
TS — Tube Steel (older designation for HSS)
MC — Miscellaneous channel
HP — H-pile section

Weld symbols

Weld symbols appear on a reference line with an arrow pointing to the joint. The symbol below the line indicates a weld on the arrow side; above the line indicates the other side.

Fillet weld — triangle symbol, most common weld type in structural steel
Groove weld — rectangle or V shape indicating weld preparation
Full penetration — double V or backing bar symbol
Plug or slot weld — circle on reference line
Seam weld — two circles on reference line
Field weld — flag on the reference line tail
All-around weld — circle at the reference line junction

Concrete and reinforcement symbols

Reinforced concrete drawings use a consistent set of abbreviations and symbols across most international standards.

or No. — rebar number (e.g. #4 bar = ½ inch diameter)

@ — spacing, e.g. #4 @ 200 means #4 bars at 200 mm spacing
EW — each way (reinforcement in both directions)
EF — each face (reinforcement on both faces of a wall)
T&B — top and bottom
BW — both ways
CL or ℄ — centreline
TYP — typical (applies to all similar conditions)
NTS — not to scale
SIM — similar

Dimension and tolerance symbols

Ø — diameter (circle with diagonal line)
R — radius
SR — spherical radius
□ — square cross-section
⌀ — alternative diameter symbol
± — plus or minus tolerance
∠ — angle
// — parallel to
⊥ — perpendicular to
≈ — approximately equal
∑ — total or sum

Section and view symbols

Section marks indicate where a section cut is taken through a drawing. The arrows show the direction of view.

Section line — cutting plane line with arrows at ends showing view direction
Detail circle — circle with leader line indicating enlarged detail
Elevation marker — circle with arrow and number indicating view direction
Grid line — bubble at end of structural grid line containing column reference
North arrow — indicates orientation on plan drawings
Revision triangle — delta symbol (▽) indicating a drawing revision

Material hatch patterns

Cross-sectional views use hatch patterns to indicate materials:

45° diagonal lines — steel or metal
Crossed diagonal lines — concrete (unreinforced)
Dots or stipple — concrete (alternative)
Brick pattern — masonry or brickwork
Horizontal lines — earth or fill material
Wavy lines — insulation
Blank (no hatch) — wood (when grain lines shown) or void

Surface finish symbols

Surface finish symbols appear on machined parts and structural connections:

√ or ∨ — surface finish required (basic symbol)
Number in symbol — required roughness value (Ra) in micrometres
Machined all over — circle on the tail of the basic symbol
No removal of material — circle added to basic symbol

Common abbreviations on structural drawings

Technical drawing symbols: ISO vs ANSI standards

Engineering drawing symbols follow different conventions depending on the standard used. In the United States, drawings typically follow ANSI/ASME Y14.5 for dimensioning and tolerancing, and AWS A2.4 for welding symbols. In the UK and Europe, BS 8888 and ISO standards apply — for example, ISO 2553 governs weld symbols and ISO 128 covers general drawing principles.

The key practical differences between ISO and ANSI technical drawing symbols are in weld notation (arrow-side vs near-side), surface finish symbology (ISO uses a tick mark with parameters; ANSI uses a checkmark), and dimensioning projection method (first-angle projection in Europe vs third-angle in the US, indicated by the truncated cone symbol on the drawing title block).

Weld symbol abbreviations and reference line notation

Weld symbols use a standardized reference line system. The tail of the reference line may include the welding process abbreviation, electrode specification, or procedure reference. Common welding process abbreviations found on structural drawings include:

How to read engineering drawing symbols

Engineering drawing symbols follow a logic that becomes easy to read with practice. Section marks always show a cutting plane line with arrows indicating the viewing direction — the number or letter at each end of the line corresponds to the section view label (e.g. “Section A-A”). Detail circles use a leader line pointing to a region and a callout number referencing a separate enlarged view at a specified scale.

Dimension symbols are always placed with the dimension value in line with the dimension line: a diameter symbol (Ø) precedes the value for circular features, while a radius symbol (R) precedes values for arcs. Tolerances appear either as plus/minus values directly after the nominal dimension or in a general tolerance block in the title block. The abbreviation TYP after a dimension means the same measurement applies to all identical features shown.

Related tools and references

Need to look up Greek letters used in structural engineering equations? Buildref has a complete symbols and references section covering Greek alphabet, mathematical symbols, and unit notation used in engineering.