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Steel Long Product Size Guide

Steel Long Product Sizes

This tool covers the full size range of steel long products, from fine wire (0.04 mm diameter) through wire rod, rebar, merchant and special bar, primary rounds, structural sections (light, medium and heavy), rail and the semi-finished products billet and bloom. Use the lookup below to identify which product category a given diameter falls into, or browse the spectrum and product cards. For a broader treatment of long product markets, economics and applications, see Long Steel Products – Essentials.

● Diameter / size lookup

mm

Diameter / cross-section – logarithmic scale 0.04 mm to 400 mm

Size boundary notes: The boundaries between wire / wire rod / bar / rebar reflect common industry convention and mill capability rather than a universal standard. The billet / bloom boundary is typically cited as 180–200 mm square but varies between producers. Sections (light, medium, heavy) are defined by maximum flange or leg width, not diameter, and are not included on the diameter spectrum above. Bar-in-coil occupies the interface between straight bar and wire rod: typically >8 mm (where coiled rebar ends) and <12 mm, it is produced as hot rolled coil on a bar mill with a coiling head and used as feedstock where coil convenience is preferred over straight lengths.

For a broader introduction to long steel products, see Long Steel Products – Essentials.

Wire

Finished
0.04–5.5 mm 0.3–4 mm (bulk of volume 1–2 mm)

Cold drawn from wire rod through tungsten carbide dies. The finest steel product by diameter. Most commercial wire is 0.3–4 mm, with the bulk of tonnage in the 1–2 mm range. Specialist applications extend down to 0.04 mm (40 micron) for high-carbon spring and music wire.

Quality / grade
High-carbon grades (>0.6% C) for springs, ropes and tyre cord. Low-carbon for general wire, mesh and nails.
Process route
Cold drawn from wire rod with intermediate annealing as required.

Cold Drawn Bar

Finished
5–12 mm

Produced by cold drawing wire rod with approximately 15–50% reduction in diameter. An alternative to hot rolled rebar used widely in Africa and developing markets where hot rolling mills are absent.

Quality / grade
Often does not meet BS 4449 in developing countries. Africa size breakdown: 5–6 mm (15%), 7–8 mm (30%), 9–10 mm (45%), 11–12 mm (10%).
Process route
Cold drawn from wire rod coil.
Notes
Overlaps with wire and small rebar size ranges.

Wire Rod

Finished
5.5–13.5 mm

Hot rolled long product supplied in coil form. Primary feedstock for wire drawing, cold heading and fastener manufacture. Produced on a continuous rod mill finishing through a no-twist block at speeds up to 120 m/s, water-cooled on a Stelmor conveyor.

Quality / grade
Low-carbon (wire, mesh, nails), medium-carbon (springs), high-carbon (tyre cord, ropes). Alloyed grades for engineering applications.
Process route
Hot rolled from billet. Below ~10 mm, rebar is often produced as coil via a rod outlet on the bar mill. Mesh is produced from 6–8 mm coil.

Rebar

Finished
6–40 mm 6–32 mm; 12 mm dominant (~50% of demand), 10 mm second

Hot rolled deformed (ribbed) bar for concrete reinforcement. The single largest product category in global long steel production. Above 10 mm produced in straight lengths; below 10 mm typically produced as coil.

Quality / grade
Western/Central/Eastern Europe: predominantly BS 4449 at 400–550 MPa. Above 600 MPa brittleness limits site bending. Soft rebar (200–250 MPa, no TMT) produced in developing markets. Ordinary rebar suits 4–5-storey construction; pre-stressed bar required for high-rise.
Process route
Hot rolled from billet. Thermomechanical treatment (TMT/QTB) applied on-line for higher-grade production.
Notes
Up to 40 mm produced, but demand above 32 mm is very limited.

Bar

Finished
13.5–110 mm 13.5–110 mm diameter; also squares, flats, hexagons

Hot rolled rounds, squares, flats and hexagons for engineering and fabrication use. Merchant bar covers general fabrication; special bar quality (SBQ) serves automotive, bearings and shafts requiring tight tolerances and clean steel practice.

Quality / grade
Wide range: carbon, alloy and engineering steels. SBQ may include peeling, straightening and non-destructive testing.
Process route
Hot rolled from billet on a bar mill.
Notes
The 13.5 mm boundary with wire rod reflects mill capability rather than product use.

Primary Rounds

Finished
110–300 mm >110 mm diameter

Large-diameter round sections for forging, ring rolling and heavy engineering. Used for shafts, axles, rings and flanges. Intermediate between bar and semi-finished products.

Quality / grade
Typically alloy or carbon engineering steel. Requires clean steel practice and often vacuum degassing.
Process route
Hot rolled from bloom on a heavy section mill, or produced by continuous casting of large-diameter rounds.

Light Sections

Finished
~20×20 mm to ~75 mm max width 20–75 mm max flange/leg width

Small structural profiles: light angles, channels and tees. Used in general fabrication, shelving and light construction.

Quality / grade
Typically S235 or S275 structural grade.
Process route
Hot rolled from billet on a light section or combination mill.
Notes
Size boundaries with medium sections are not standardised across producers.

Medium Sections

Finished
~75×75 mm to ~150–200 mm max width 75–150 mm max flange/leg width

Medium-weight structural profiles: angles, channels, beams and tees. Common in construction, industrial buildings and infrastructure.

Quality / grade
S235, S275, S355.
Process route
Hot rolled from billet or bloom on a section mill.

Heavy Sections

Finished
~150–200 mm+ flange width to Up to ~1,000 mm serial depth 150 mm+ flange width; 8–625 kg/m

Large structural I- and H-sections for heavy building frames, bridges and crane girders. Standard lengths 12 m (truck) or 18 m (rail transport). Cooling beds on heavy section mills are typically 36 m, permitting 36 m lengths cut to two or three pieces. Often share a rolling line with rail production.

Quality / grade
S355 standard; S420, S460 and higher available. Z-grade (through-thickness) for welded connections.
Process route
Hot rolled from bloom on a reversing heavy section (universal) mill with edgers. Straightened in a roller straightener after cooling.
Notes
A 36 m cooling bed serves both 36 m rail and 12/18 m heavy section production.

Rail

Finished
~49 kg/m (standard) to ~60 kg/m (high-speed) 12 m, 18 m, 24 m, 36 m, 72 m lengths; up to 120 m (advanced mills)

Asymmetric I-section profile carrying and guiding wheel loads. Head hardened to resist wear; foot fixed to sleepers. Standard conventional track: ~49 kg/m. High-speed rail: ~60 kg/m. The most advanced mills (VAI Schienen technology) produce 120 m lengths for continuously welded high-speed track.

Quality / grade
R260 (260 HB) standard. R320Cr and R350HT (heat-treated) for heavy-haul and high-speed. Head-hardened rail for curves and high-tonnage routes.
Process route
Hot rolled from bloom on a combined heavy section/rail mill. Long rail requires on-line or off-line heat treatment.
Notes
Rail mills and heavy section mills often share a common rolling line and 36 m cooling bed.

Billet

Semi-finished
100–200 mm 100–180 mm square; up to ~200 mm square

Square or near-square semi-finished product, continuously cast from liquid steel. Feedstock for rod, bar, rebar and light/medium section rolling mills. Typically 100–120 mm square up to a maximum of ~180–200 mm square, above which the product is classified as bloom.

Quality / grade
Chemical composition controlled to suit downstream product. Inspected for surface defects and internal soundness.
Process route
Continuously cast via tundish through an oscillating copper mould. Cut to length by torch cutter.
Notes
The billet/bloom boundary is not universally fixed; 180–200 mm square is the most common convention.

Bloom

Semi-finished
180–400 mm 180–360 mm square; up to ~400 mm square

Larger square or rectangular semi-finished product, above billet in cross-section. Feedstock for heavy section, rail, primary round and special bar rolling mills; also input to forging operations. Greater importance is placed on internal soundness given the larger cross-section.

Quality / grade
As for billet, with greater scrutiny of centreline quality for demanding downstream applications.
Process route
Continuously cast on a bloom caster, often with soft reduction to improve centreline quality. Some blooms still produced by ingot rolling on a primary mill.

Frequently Asked Questions

What is the difference between billet and bloom?

Both billet and bloom are semi-finished continuously cast products with a square or near-square cross-section. Billet is smaller, typically 100–180 mm square (up to ~200 mm), and is the feedstock for rod, bar and rebar rolling mills, continuously cast on a billet caster. Bloom is larger, typically 180–360 mm square (up to ~400 mm), and feeds heavy section, rail, primary round and forging operations. The boundary is not universally standardised; 180–200 mm square is the most widely used convention.

What diameter is wire rod?

Wire rod is hot rolled long product supplied in coil form, in the diameter range 5.5–13.5 mm. Below 5.5 mm the product is classed as drawn wire; above approximately 13.5 mm it is classed as bar. The boundaries reflect mill capability: wire rod is produced on a high-speed rod block; bar is rolled on a bar mill in straight lengths.

What are the standard rebar diameters?

Rebar is the largest single category by volume within long products capacity, and is produced in diameters from 6 mm to 40 mm. The most common stock sizes are 6, 8, 10, 12, 14, 16, 18, 20, 25 and 32 mm. The 12 mm diameter accounts for approximately 50% of total rebar demand; 10 mm is the second most popular. Above 32 mm demand is very limited. Below about 10 mm, rebar is typically produced in coil (including 6–8 mm mesh feedstock); above 10 mm it is produced in straight lengths.

How heavy is railway rail?

Standard conventional track rail weighs approximately 49 kg/m. High-speed rail is approximately 60 kg/m. Rail is produced in lengths of 12 m, 18 m, 24 m, 36 m and 72 m. The most advanced mills – using VAI Schienen technology – produce 120 m lengths for continuously welded high-speed track.

What is the difference between bar and wire rod?

The conventional boundary is approximately 13.5 mm diameter. Wire rod (5.5–13.5 mm) is produced in continuous coil on a high-speed rod block. Bar (13.5–110 mm and above) is hot rolled in straight lengths on a bar rolling mill. The distinction reflects mill design and capability as much as end-use.

What is cold drawn bar?

Cold drawn bar is produced by drawing wire rod through dies to reduce its diameter by approximately 15–50%, producing a smooth or lightly deformed bar in the 5–12 mm range. It is an alternative to hot rolled rebar in markets – particularly parts of Africa – where hot rolling mills are not present. It does not typically meet BS 4449 in developing countries. The most common sizes are 9–10 mm (~45% of demand in African markets).

What defines light, medium and heavy structural sections?

The classification is based on maximum flange or leg width. Light sections: approximately 20×20 mm to 75×75 mm maximum width. Medium sections: approximately 75×75 mm to 150–200 mm maximum width. Heavy sections: 150 mm or 200 mm and above in maximum width, including large universal beams and column sections. These boundaries are not universally standardised and can differ between producers.

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