I-Beam Size Chart: Dimensions for Standard Structural Members

What an I-beam size chart actually shows

An I-beam size chart is a table that lists the physical dimensions of structural I-shaped members. The basic entries are nominal size, depth, flange width, web thickness, and weight per length. These numbers define the member’s geometry, which determines its moment of inertia, shear capacity, and deflection behavior.

When a buyer asks for “a 200 mm I-beam,” the supplier needs to know which standard applies. Different regions and mills use different naming conventions, so the same nominal size can have different flange and web dimensions. A size chart bridges that gap by placing common standards side by side.

The chart also helps with logistics. A heavier section needs a larger crane, a stronger transport tie-down, and a bigger shop floor footprint. Knowing the weight per meter before ordering prevents a last-minute change that delays the schedule.

How the main dimensions affect selection

The depth of the beam is the primary driver for bending capacity. A deeper section resists bending better because the material sits farther from the neutral axis. If the span is long or the load is high, a deeper I-beam reduces the required flange area and can lower the total weight.

Flange width controls lateral stability and shear transfer. A wider flange gives the connection area for bolts or welds and improves resistance to buckling of the flange. Narrow flanges are easier to fit in tight building bays but may need bracing or stiffeners.

Web thickness governs shear and web buckling. A thin web is lighter, which helps with weight and cost, but it may buckle under high shear or local bearing loads. At a column base or a heavy load point, the web may need to be thickened or reinforced.

Weight per length is not just a number on a spec sheet. It drives shipping cost, erection sequence, and shop floor handling. A 50 mm increase in depth can add a meaningful amount of steel per meter, which changes the number of trucks and the size of the hoist.

Nominal size versus actual size

The nominal size is the reference label used in drawings and purchase orders. For many I-beams, the nominal size is based on the depth in millimeters or inches. For example, a member marked as 200 mm usually has an actual depth close to 200 mm, though the exact figure depends on the standard.

The actual dimensions are what matter for fabrication. A flange width that is 2 mm wider changes the bolt hole layout. A web that is 1 mm thinner changes the shear capacity slightly and may affect the fit of a stiffener.

When comparing two suppliers, ask for the actual mill dimensions, not just the nominal label. The mill test certificate lists the measured values. If the project uses a standard connection detail, even small deviations can force a field modification.

How to read a standard I-beam size table

A typical I-beam size table has columns for nominal size, depth, flange width, web thickness, and weight per unit length. Some tables add the section modulus or moment of inertia, which are useful for hand calculations.

The table below shows a simplified comparison of common nominal sizes. The dimensions are representative of standard structural profiles and are used here to illustrate how the geometry changes as the nominal size increases. The values do not represent a single mill’s exact output, so always check the specific standard for the project.

Nominal Size	Depth (mm)	Flange Width (mm)	Web Thickness (mm)	Weight per meter (approx.)
100 mm	100	100	6	9.5
150 mm	150	120	8	16.5
200 mm	200	150	10	25.5
250 mm	250	180	12	36.5
300 mm	300	210	14	49.5
350 mm	350	240	16	64.5

The trend is clear. As the nominal size increases, the depth, flange width, web thickness, and weight all rise. The weight increase is not linear. A 50 mm jump in depth can add more steel than the previous 50 mm jump because the flanges and web get proportionally larger.

A worked example in plain words

Imagine a project needs a beam for a 6 meter span with a uniformly distributed load. The engineer selects a 200 mm I-beam based on preliminary bending and deflection checks. The drawing calls for the standard 200 mm profile with a 150 mm flange width and a 10 mm web thickness.

The buyer goes to the I-beam size chart to confirm the weight. The table shows roughly 25.5 kg per meter. For a 6 meter length, the beam weighs about 153 kg. That weight is manageable for a small mobile crane and can be lifted with a single sling.

If the buyer instead chose a 250 mm I-beam for the same span, the weight would jump to about 36.5 kg per meter, or 219 kg for 6 meters. The larger beam may be needed for a heavier load, but if the load is the same, the extra weight increases handling cost and may require a bigger crane. The size chart makes that trade-off visible before the order is placed.

Common mistakes when using size charts

One frequent error is assuming that all 200 mm I-beams are identical. They are not. Different standards and mills may have different flange and web dimensions. A 200 mm beam with a 150 mm flange is not the same as one with a 130 mm flange, even though both are labeled 200 mm.

Another mistake is relying only on the nominal size. The connection details on the drawing may specify bolt hole positions that depend on the actual flange width. If the mill delivers a section with a slightly different flange width, the connection plate may not fit without modification.

A third error is ignoring the weight. A project team may select a larger section to be safe, but the extra weight can cause problems in the shop and on site. A size chart helps the team compare the weight increase against the capacity gain.

How to verify dimensions before fabrication

Before cutting, welding, or ordering connection plates, the buyer should request the mill dimensions for the specific lot. The mill test certificate or the mill’s standard specification lists the actual measured values. If the project is international, confirm that the standard referenced in the drawing matches the standard used by the mill.

In the shop, a quick visual check against the size chart can catch a wrong delivery. If the flange width is obviously narrower than expected, stop the cut. A single wrong section can force a rework that delays the whole package.

For critical connections, use the actual dimensions from the certificate to lay out the bolt holes. This removes guesswork and ensures the field assembly goes smoothly.

When to go beyond a basic size chart

A basic I-beam size chart is enough for many standard projects. But for high-rise frames, long-span bridges, or heavy industrial plant floors, the engineer may need more than just depth and weight. The section modulus, moment of inertia, and shear capacity become the primary selection tools.

In those cases, the size chart is a starting point. The engineer uses the geometric properties to compare several nominal sizes and pick the one that meets the capacity and deflection limits with the least weight. The size chart still helps, but it is one part of a larger calculation.

For projects with strict cost targets, a weight comparison across several sizes can reveal a more efficient option. Sometimes a slightly larger section is cheaper than a smaller one plus additional stiffeners and bracing. The size chart makes that comparison quick and easy.