I-Beam
A steel member with an I-shaped cross-section, priced by weight per foot.
Quick Answer
An I-beam is a structural steel member whose cross-section looks like the letter I: two flanges joined by a web. In US steel tables the true I-beam is the S-shape, with tapered flanges, while the wide flange W-shape is more common. Estimators take either off by length and weight per foot.
The Full Picture
"I-beam" is a common name, not a precise designation. In AISC shape tables, the shape with sloped inner flange faces is the S-shape (American Standard beam), designated like S12x31.8, meaning about 12 inches deep and 31.8 pounds per foot. The more common wide flange W-shape has parallel flange faces and wider flanges, designated like W16x40. When someone says "I-beam" on a bid, ask or look up which one the drawings show.
The distinction matters because the shapes behave differently and are priced differently. S-shapes have narrower, tapered flanges and are less common in new buildings; they appear in older construction, crane runways, and special cases. W-shapes dominate modern framing. In the US, ASTM A992 is the preferred grade for W-shapes, while S-shapes are still frequently specified as A36 or a higher grade, so confirm grade against the general notes.
On the drawings, beams are tagged on the framing plans with shape, size and often camber or stud counts, and the structural general notes list grades. Details show end connections, such as shear tabs or clip angles, and bearing on walls or columns. Estimators should also review lintel and opening schedules, because beams over openings can be hidden in architectural sheets.
Takeoff is by linear foot per size, multiplied by the weight per foot, producing pounds and tons. Count pieces too, because fabrication and erection scale with piece count. Cuts, copes, holes, camber and splices add shop labor that is not visible in the weight alone. Mill length and cut-off waste are handled by the fabricator, so confirm whether your price assumes net or ordered weight.
Real Examples
Common Misconceptions
People assume: An I-beam and a wide flange beam are the same thing.
Actually: Both are I-shaped, but in US tables the S-shape has tapered flanges and the W-shape has parallel flanges. They have different dimensions and weights, so they are not interchangeable without engineer approval.
People assume: A beam's name tells you its weight.
Actually: The number after the "x" is pounds per foot, but only for the shape listed. A W12x26 and an S12x31.8 are both 12 inches deep and weigh differently.
People assume: Deeper always means heavier.
Actually: Weight per foot depends on flange width and thickness as well as depth, so each size must be read from the shape table.
Does MeltPlan Solve This?
Partially — adjacentMeltPlan's takeoff pulls quantities from PDF plans and US-based estimators review and adjust them, which covers measuring and counting beams from the framing plan. Choosing shapes and pricing steel stays with the estimator.
Measure beam lengths and counts from structural plans →Frequently Asked Questions
Is an I-beam the same as an H-beam?
Not exactly. Both are I- or H-shaped. In the US, the common H-looking shapes are W-shapes (wide flange), and HP-shapes are bearing pile sections. H-beam is more of an international term.
What does S12x31.8 mean?
It is an S-shape about 12 inches deep that weighs 31.8 pounds per linear foot. The weight per foot is used to convert length into pounds.
How do you calculate the weight of an I-beam?
Multiply the length in feet by the weight per foot for the specific shape from the AISC shape tables. Divide by 2,000 for tons.
What grade steel is an I-beam?
It depends on the shape and the drawings. W-shapes are normally A992, S-shapes are often A36 or a higher grade. Check the structural general notes.
Where do I find beam sizes on the drawings?
On the structural framing plans, with schedules, elevations and connection details as backup. Lintel and opening beams can also appear on architectural wall sections.