Structural steel has framed commercial buildings since the Rand McNally Building went up in Chicago in 1890, and steel remains a preferred material for major construction because it combines lightness, high strength, and fast erection. Steel bonds well to concrete, arrives at the site in predictable sections, and lets contractors close in a building in weeks rather than months. Among the most common rolled sections are the H-beam and the I-beam, two members that look alike at a glance but behave differently under load. Choosing between them comes down to how each shape distributes weight, and comparing weight, web center, spans and flanges is where most specification decisions start.
This article defines both members, compares their strength and cost, and walks through the selection steps used in practice.
What Is an H-Beam?
An H-beam is a rolled steel member whose cross-section looks like a capital H. The vertical element is the web, and the horizontal plates at the top and bottom are the flanges. H-beams have wide flanges of roughly equal thickness to the web, and the flange faces are parallel rather than tapered, which makes the section look square and balanced.
The wide flanges give the H-beam high strength in both bending directions and make it an efficient column section. Later sections cover key differences, uses and structural selection in detail, but the short version is that an H-beam resists heavy vertical loads and works well when load can arrive from more than one direction.
H-Beam Dimensions and Sizes
H-sections are produced in a wide size range. In European practice, the HEA, HEB, and HEM series run from about 100 mm nominal height up to 1,000 mm, and each series trades weight against bending capacity. In North America, the equivalent members are wide-flange W-shapes, designated by nominal depth and weight per foot, such as W12x26. Square H-sections, where the flange width equals the section height, are common in column applications because the two axes behave almost identically.
Reading an H-Beam Size Designation
A designation such as HEB 300 tells you the family (HE), the series (B, the medium-weight combination of web and flange), and the nominal height in millimetres (300). In the imperial W-shape system, W12x26 means a nominal depth of 12 inches and a weight of 26 pounds per foot. The same reading rules apply across the HEA, HEB, HEM, and W families.
What Is an I-Beam?
An I-beam takes its name from its cross-section, which looks like a capital I. The classic I-beam, also called an American standard beam or S-shape, has flanges that taper in thickness from the web toward the outer edge. Because the flanges are narrower and the section is lighter than an equivalent H-beam, I-beams are economical for members that bend mainly in one direction, such as floor beams and roof purlins.
Contractors preparing steel estimates often start with a bar bending schedule for beam steel quantity before ordering any member, because the schedule fixes the number, length, and shape of every piece of reinforcement and structural steel in the frame.
I-Beam, S-Beam, and W-Beam Naming
Rolled steel naming causes most of the confusion between H and I sections:
- S-shape (American Standard): the true I-beam, with tapered flanges and a thicker web.
- W-shape (wide flange): parallel flanges, often wider than an S-shape of the same depth; in North America this is the standard framing member and it resembles an H-beam.
- H-shape: the widest-flange family, used mostly for columns and heavy transfer members.
How an I-Beam Carries Load
In a beam loaded from above, the flanges carry the bending stresses, with compression at the top and tension at the bottom, and the web carries the shear. Because the flanges of an I-beam are narrow, the section is very efficient for bending about its strong axis but comparatively weak when load tries to bend it sideways. That is why I-beams are almost always installed with the web vertical.
Key Differences Between H-Beam and I-Beam
The practical differences come down to geometry. H-beams have wider, parallel flanges and a heavier cross-section per metre; I-beams have narrower, tapered flanges and weigh less. When structural steel sections are compared for building construction, the deciding questions are load direction, span length, and budget.
| Feature | H-Beam | I-Beam |
|---|---|---|
| Cross-section shape | Capital H | Capital I |
| Flange width | Wide, similar to section height in square sections | Narrow relative to depth |
| Flange taper | Parallel faces, no taper | Tapered from web to edge (S-shape) |
| Weight per metre | Heavier for the same nominal depth | Lighter for the same nominal depth |
| Bending strength | High about both axes | High about the strong axis only |
| Typical use | Columns, transfer beams, heavy frames | Floor beams, purlins, light frames |
| Relative cost | Higher material cost per metre | Lower material cost per metre |
Which Is Heavier?
Weight differences are large. In European series, an HEB 300 weighs about 117 kg per metre and an HEA 300 about 88 kg per metre, while an IPE 300, an I-section of the same nominal depth, weighs about 42 kg per metre. The H-beam puts roughly two to three times more steel into the same nominal depth, which is exactly why it carries more load and costs more.
Cost Considerations
On a per-tonne basis, H-beams and I-beams cost similar amounts at the mill; the difference shows up in the bill of quantities. A frame that uses fewer, heavier H-beams can save on connections, welding, and erection time, while a light I-beam frame spends less on material but more on pieces and labour. Running both options through a quantity take-off before ordering usually settles the choice.
Strength and Load-Bearing Behavior
Asked which is stronger, most engineers answer that it depends on the direction of the load. An H-beam is stronger for vertical compression and column service because its wide flanges resist buckling about both axes. An I-beam is extremely strong in bending about its strong axis but comparatively weak about its weak axis, so it suits floor beams and other members that are braced against sideways movement.
The same cross-section logic shows up in hand tools: comparing an I-beam vs box beam level for accuracy, sizes, and what to check explains why level manufacturers choose one profile over the other. Stiffness comes from the same web-and-flange geometry scaled down to a tool body.
Strong Axis vs Weak Axis
Every beam section has two bending axes: the strong axis (X-X), which runs through the web, and the weak axis (Y-Y), which runs through the flanges. For an I-beam, the moment of inertia about X-X is many times larger than about Y-Y, so the member must be oriented with the web vertical and braced against sideways buckling. An H-beam, with its wider flanges, has a much smaller gap between the two values, which makes it forgiving when loads arrive from several directions.
Buckling and Column Behaviour
Columns fail by buckling long before the steel yields, and the resistance to buckling depends on the slenderness ratio, which is the effective length divided by the radius of gyration of the section. Because the H-beam spreads its material across wide flanges, its radius of gyration is similar in both directions, so it resists buckling equally well no matter which way it is loaded. That is why H-sections dominate column schedules and I-sections dominate beam schedules.
Applications and How to Choose Between Them
H-beams appear in multi-storey columns, transfer girders, bridge piers, and heavy industrial frames. I-beams appear in floor framing, roof purlins, mezzanines, and residential steel structures where the loads are lighter and the spans are supported at both ends. Whatever member you pick, the connections matter just as much, and reviewing the common types of steel beam connections before detailing prevents field clashes.
Step-by-Step: Selecting a Beam Section
- Define the span and the loads: dead load, live load, and any point loads from equipment or partitions.
- Check the deflection limit; L/360 for floors under brittle finishes and L/240 for general framing are common starting points.
- Compute the required section modulus and moment of inertia for the governing load combination.
- Choose the lightest section from the appropriate series that meets both strength and deflection.
- Verify the member fits the connection details and column sizes at both ends before ordering.
Spanning and Support Rules
Rolled beams are economical over spans of roughly 6 to 12 metres (20 to 40 feet) in most buildings. Longer spans push the section size up quickly, and at some point trusses, plate girders, or castellated beams become cheaper than a single rolled section. Support conditions matter too: a simply supported beam of a given section carries about half the load of a continuous beam of the same section, so continuity should be detailed wherever it is practical.
Weights, Costs, and Specification Notes
Unit weights drive both design and procurement. Standard tables list H-beam and I-beam mass per metre, and the specifier should read the series carefully, because HEA, HEB, and HEM sections share the same nominal depth but differ by 30 to 40 percent in weight. Ordering by nominal size alone is a common and expensive error.
Tracing the evolution of beam design from riveted plate girders to rolled H sections explains why standardisation made steel framing cheaper. Once mills could roll wide flanges in one pass, the industry stopped building up members from plates and rivets, and the modern H and I families emerged. The next time a steel order crosses your desk, the shape of the letter in the cross-section tells you most of what you need to know about how the member will work.
What to Confirm in the Drawings
- Nominal depth and series (HEA, HEB, HEM, W, S) match the structural notes.
- Flange orientation is drawn correctly; a rotated I-beam loses most of its bending strength.
- Camber, coping, and connection details agree with the shop drawings.
- Surface protection such as primer, galvanizing, or intumescent coating is specified for the environment.