Structural Steel Grades in Canada: 350W, 300W and A992

Canadian structural steel is specified to CSA G40.21, and the workhorse grade is 350W: a weldable steel with a minimum yield strength of 350 MPa. Wide-flange beams are the exception in practice. Most W-shapes sold in Canada today are rolled to the US grade ASTM A992 and certified at the same time to CSA G40.21 345WM, both with a 345 MPa (50 ksi) minimum yield. 300W (300 MPa) shows up mainly on plate, flat bar and light shapes, and ASTM A36 (250 MPa) on older drawings and some plate and bar.

This guide gives the grade chart, explains how the names work, and covers what the grade means for beams, posts and the Ontario Building Code.

Structural steel grades chart

The bracketed names (50W, 44W, 50WM) are the older imperial-style names based on yield in ksi. Mills and fabrication shops still use both, so "44W plate" and "300W plate" are the same thing.

This chart covers the common grades for buildings and houses. CSA G40.21 also includes higher-strength and special-purpose grades used in bridges, heavy industrial work and cold-weather structures. For tube, see our HSS steel grades guide, and for plate, our steel plate grades guide.

How to read a Canadian grade name

A CSA G40.21 grade has two parts: a number and one or more letters.

• The number is the minimum yield strength in megapascals. 350W means the steel will not yield below 350 MPa. 300W means 300 MPa.
• W means weldable steel. It is the ordinary structural type, and the one almost every building drawing calls for.
• T means impact tested for notch toughness. 350WT, for example, is 350W with Charpy test requirements, specified for some cold-exposed or dynamically loaded members such as bridges and crane girders.
• A and AT are atmospheric corrosion-resistant grades (weathering steel), used mainly in bridges and exposed structures where the steel is left unpainted.
• WM is the grade family added in the 2013 edition of CSA G40.21 to line up with ASTM A992. That edition, G40.21-13, is the one the 2024 Ontario Building Code references.

US grades work differently. ASTM A992, A572 and A36 are separate specifications, and the yield strength is either built into the spec (A992 and A36) or named as a grade within it (A572 Grade 50).

Wide-flange beam grades: A992, 345WM and 350W

Searches for "steel beam grades" or "I-beam grade" are usually about wide-flange beams, and this is where the Canadian and US systems meet.

ASTM A992 is the standard material specification for wide-flange shapes in North America. Its key values:

• Minimum yield strength 345 MPa (50 ksi).
• Minimum tensile strength 450 MPa (65 ksi).
• A cap on the ratio of yield to tensile strength (0.85), which gives designers more predictable ductility.

CSA G40.21 345WM was written to match A992, so one beam can carry both certifications. Nucor-Yamato, a large US wide-flange mill that ships into Canada, announced in 2014 that it was moving its Canadian production to the new 345WM grade, and that its mill test reports would list ASTM A992, ASTM A709 Grade 50S and CSA G40.21 345WM together. Its customer letter also said the older 350W certification would no longer be offered on its grade sheets.

That leaves an awkward detail for anyone ordering from older drawings: many drawings still say 350W for W-beams, but much of the W-shape supply is certified to 345WM and A992. The difference is 5 MPa of minimum yield. Whether that is acceptable is a question for the engineer of record, not the supplier. In practice, designers answer it once on the drawings or in a substitution request, and the fabricator orders accordingly.

ASTM A36 was once the common beam grade and still turns up in two places: drawings for older buildings, and imported or small-run sections. At 250 MPa minimum yield it is a lower-strength steel, so a beam designed as 350W or A992 cannot be swapped for an A36 beam of the same size without a recheck.

What about "W-beam yield strength"? There isn't a single number, because yield strength belongs to the grade, not the shape. A W200x27 in A992 has a 345 MPa minimum yield; the identical shape in A36 has 250 MPa.

The Ontario Building Code and 350W

For houses and small buildings, the 2024 Ontario Building Code lets designers pick steel beams from span tables in Part 9 (Article 9.23.4.3., with Table 9.23.4.3. for floors and Tables 9.23.4.3.-A to 9.23.4.3.-J for roofs and floors). Sentence 9.23.4.3.(2) says those beams must at least meet the requirements for Grade 350W steel in CSA G40.21.

The explanatory note to the floor table lists the assumptions behind it, including a 350 MPa yield strength, a laterally supported top flange and a deflection limit of span/360. Our steel beam span tables guide walks through those tables.

Two practical points for homeowners and contractors:

1. If the beam came from the OBC tables, the grade matters. The table spans assume 350 MPa steel. If the beam offered is certified only to A992 or 345WM, ask your designer or building department to confirm it is acceptable before it is installed. Do not assume.
2. Ask for the mill test report. It is the only document that shows which grades the steel actually meets. An inspector or engineer may ask for it.

Higher grade is stronger, not stiffer

All structural steel grades have essentially the same modulus of elasticity, about 200 000 MPa. That has a consequence people often miss:

• A higher grade raises strength: the load at which the beam yields or a column fails.
• A higher grade does nothing for deflection. A 350W beam and an A36 beam of the same size sag exactly the same amount under the same load.

In houses, beam size is often governed by deflection and vibration rather than strength, which is one reason the OBC tables include a deflection limit. If a beam bounces or sags, the fix is a deeper or heavier section or a shorter span, not a higher grade. The same logic applies to channels and angles, covered in our steel channel grades guide.

Grades for other shapes, and what is not structural steel

Each shape family has its usual grades in Canada:

• HSS (tube): CSA G40.21 350W, Class C (cold-formed) or Class H (stress-relieved), or ASTM A500 Grade C. The design wall thickness differs between the two standards, which matters for engineering.
• Channels and angles: CSA G40.21 300W or 350W, ASTM A572 Grade 50, or A36. Multi-certified material is common.
• Plate and flat bar: CSA G40.21 300W (44W) or 350W, ASTM A36 or A572 Grade 50.
• H-piles: usually high-strength grades such as ASTM A572 Grade 50, as the project's pile specification requires.

Two things that are not "structural steel grades" in this sense:

• Rebar is made to a different standard, CSA G30.18, with grades such as 400W and 500W. See rebar grades in Canada.
• Bolts and anchor rods have their own ASTM specifications. A 350W beam does not tell you anything about the bolts that connect it.

Imported steel sometimes arrives with European grades such as S355, which Nucor-Yamato also lists among the certifications it can provide on certain sections. European grades are not automatically equivalent to Canadian ones for design. If imported material is offered, the engineer decides whether it can be used and on what basis.

Putting the right grade on the order

To avoid delays and rejected material:

1. Show the grade on the drawings, per shape family. "Structural steel to CSA G40.21 350W unless noted, W-shapes to ASTM A992 or CSA G40.21 345WM" is a typical general note.
2. Ask for mill test reports when the project needs them, and keep them in the job file.
3. Check the certified grade, not just the measured yield. A heat of A36 steel that happens to test above 350 MPa is still certified A36.
4. Get substitutions approved in writing by the designer or engineer.
5. For existing buildings, the grade of old steel is often unknown. The engineer may use conservative assumptions or have samples tested before relying on it, especially if anything is to be welded to it.

Steel supplied to the grade on your drawings

We supply and fabricate beams, posts, plates, channels and lintels for residential, commercial and industrial projects, cut, drilled and welded to the shop drawings we prepare in-house. If you are not sure which grade your drawings call for, send them over and we will read them with you; any substitution still goes back to your designer. Send your drawings for a free take-off and quote, or see our steel products.