I-Beams — ISMB Dimensions & Properties

// Indian Standard Medium Beams (ISMB)

Designation	Depth (mm)	Flange (mm)	Web (mm)	tf (mm)	Wt (kg/m)	Area (mm²)
ISMB 100	100	75	4.0	7.2	11.5	1460	View →
ISMB 125	125	75	4.4	7.6	13.0	1660	View →
ISMB 150	150	80	4.8	7.6	14.9	1900	View →
ISMB 175	175	90	5.5	8.6	19.3	2460	View →
ISMB 200	200	100	5.7	10.8	25.4	3229	View →
ISMB 225	225	110	6.5	11.8	31.2	3970	View →
ISMB 250	250	125	6.9	12.5	37.3	4750	View →
ISMB 300	300	140	7.7	13.1	44.2	5630	View →
ISMB 350	350	140	8.1	14.2	52.4	6670	View →
ISMB 400	400	140	8.9	16.0	61.5	7840	View →
ISMB 450	450	150	9.4	17.4	72.4	9230	View →
ISMB 500	500	180	10.2	17.2	86.9	11070	View →
ISMB 550	550	190	11.2	19.3	103.7	13210	View →
ISMB 600	600	210	12.0	20.8	122.6	15619	View →

All dimensions per IS 808 : 1989. Click any row for the complete specification including sectional properties, plastic moduli, radii of gyration, torsional constants, and downloadable PDF spec sheet.

What is an ISMB I-Beam?

An ISMB (Indian Standard Medium Weight Beam) is a hot-rolled structural steel section with a cross-section shaped like the letter I. The "medium weight" designation distinguishes it from other Indian standard beam families: ISLB (light), ISWB (wide flange), ISJB (junior), and ISHB (heavy). ISMB is the most widely used structural beam section in Indian construction — found in nearly every steel building, industrial structure, bridge, and infrastructure project across the country.

The defining feature of an I-beam is its extremely high moment of inertia about the strong axis (X-X) for a given cross-sectional area. By placing most of the steel in the two flanges far from the neutral axis, the I-beam maximises bending resistance while minimising self-weight. This makes ISMB the section of choice for any application where the dominant load is bending — joists, lintels, simply supported beams, purlins, and the main flexural members of trusses and frames.

Quick rule of thumb: Use ISMB I-beams for bending-dominated applications. Use ISHB H-beams when the section also carries significant axial compression (columns, struts, props).

When to use ISMB

ISMB is the default structural beam in Indian construction for spans between roughly 3 and 12 metres. The 14 standard sizes cover everything from light residential floor joists (ISMB 100, 125, 150) through industrial purlins and runway beams (ISMB 200–350) to heavy primary girders in multi-storey construction (ISMB 400–600). Beyond ISMB 600, designers typically move to welded plate girders or composite sections.

Typical applications by size range

ISMB 100–150 — light floor joists, lintels over door and window openings, residential mezzanines, equipment supports, light industrial framing
ISMB 175–250 — secondary beams in commercial buildings, purlins for industrial sheds, light crane runway beams, staircase stringers
ISMB 300–400 — primary floor beams in multi-storey buildings, bridge stringers, main beams in industrial structures, transfer girders for medium loads
ISMB 450–600 — heavy floor beams in commercial high-rises, main girders in industrial structures, bridge cross girders, crane gantry beams for medium-capacity cranes

International equivalents

ISMB sections do not have direct one-to-one equivalents in international standards because every standards body uses different proportions. The closest functional equivalents based on depth and weight are:

ISMB (India)	IPE (Europe)	UB (UK)	W-shape (USA)	JIS H (Japan)
ISMB 100 @ 11.5	IPE 100	—	W4×13	H 100×100
ISMB 150 @ 14.9	IPE 140	152×89×16 UB	W6×12	H 150×100
ISMB 200 @ 25.4	IPE 200	203×102×23 UB	W8×18	H 200×100
ISMB 250 @ 37.3	IPE 240	254×102×28 UB	W10×26	H 250×125
ISMB 300 @ 44.2	IPE 300	305×127×37 UB	W12×30	H 300×150
ISMB 400 @ 61.5	IPE 400	406×140×46 UB	W16×40	H 400×150
ISMB 500 @ 86.9	IPE 500	457×191×67 UB	W18×60	H 500×200
ISMB 600 @ 122.6	IPE 600	610×229×113 UB	W24×84	H 600×200

Equivalence is approximate, based on closest matching depth + weight. ISMB has tapered flanges (8° slope per IS 808), while IPE, UB, and W-shapes have parallel flanges. Always verify exact section properties from the actual standard before substituting in design calculations.

Material grades

ISMB sections are produced in structural steel grades specified by IS 2062 : 2011 — Hot rolled medium and high tensile structural steel. The most common grades are:

Grade	Yield (MPa min)	Tensile (MPa min)	Elongation %	Typical use
E 250 (Fe 410W)	250	410	23	General construction (default grade in India)
E 350	350	490	22	Multi-storey buildings, industrial structures
E 410	410	540	20	Heavy-duty beams, weight-critical designs
E 450	450	570	20	Bridges, offshore structures
E 550	550	650	18	High-strength applications, long spans

Higher grades allow lighter sections to carry the same bending moment, but come at a price premium and may require more careful welding procedures. For most building applications in India, E 250 remains the default unless engineering analysis shows that a higher grade reduces overall steel tonnage by more than the cost premium.

Ordering specification

When ordering ISMB sections from a rolling mill, the standard specification format is:

Example: "ISMB 300 @ 44.2 kg/m, Grade E 250 to IS 2062, length 12 metres random, mill certificate as per IS 1852, BIS standard tolerance class A."

The key elements of an ISMB order are: designation (section size), grade (material per IS 2062), length (standard 10–13 m random or cut-to-length at premium), tolerance class (Class A tighter for structural use, Class B looser per IS 1852), surface condition (black mill finish, shot blast cleaned, or pre-primed), and mill test certificate (TC1, TC2, or TC3 traceability per IS 1387).

Frequently asked questions

+ What does ISMB stand for?

ISMB stands for Indian Standard Medium Weight Beam. The "medium weight" refers to its position between lighter sections (ISLB — Light Beams, ISJB — Junior Beams) and heavier sections (ISWB — Wide Flange Beams, ISHB — Heavy Beams). ISMB is the most commonly used structural I-beam in Indian construction, dominating roughly 80% of structural steel applications by volume.

+ Why does ISMB have tapered flanges?

ISMB sections (and most older I-beam standards including DIN 1025 IPN, JIS I-beams, and the original American S-shapes) have flanges that taper at approximately 8° from the centreline outward. The taper is a legacy of two-high mill rolling, where the slope helps the rolled beam release cleanly from the grooves in the rolls. Modern parallel flange sections like IPE and W-shapes are rolled in universal mills with both horizontal and vertical rolls, which can produce parallel flanges directly. Tapered flanges are slightly less efficient structurally (more material near the neutral axis) but cheaper to manufacture in conventional rolling mills.

+ What is the difference between ISMB and ISWB?

ISWB (Indian Standard Wide flange Beam) sections have wider flanges and slightly higher minor-axis stiffness compared to ISMB of the same depth. For example, ISMB 400 has a flange width of 140 mm, while ISWB 400 has a flange width of 200 mm. ISWB is preferred when the beam needs to resist torsion or lateral loads, or when minor-axis bending stiffness matters. ISMB remains the cost-effective default for pure strong-axis bending.

+ Are ISMB sections weldable?

Yes — all ISMB sections in standard IS 2062 grades (E 250 through E 550) are fully weldable using shielded metal arc welding (SMAW), gas metal arc welding (GMAW/MIG), or submerged arc welding (SAW). The carbon equivalent (CEV) of E 250 grade is typically below 0.42, which means no preheat is required for sections up to 25 mm thick. For higher grades or thicker sections, preheating may be specified per IS 9595.

+ What is the maximum span for an ISMB beam?

The maximum economical span depends on the load and grade, but as a rough guide: ISMB 300 spans about 6 metres for typical floor loads, ISMB 400 spans 8 metres, ISMB 500 spans 10 metres, and ISMB 600 spans 12 metres. Beyond 12 metres, plate girders or composite sections become more economical. For cantilever spans, the limits are roughly half of these values due to higher deflection and instability concerns.

+ What rolling mill equipment produces ISMB sections?

ISMB sections are produced in section mills — typically a combination of roughing stands (2-high reversing or 3-high), intermediate finishing stands, and a final finishing stand, all with shaped rolls grooved to the I-beam profile. The 8° flange taper allows the rolled section to be produced on conventional 2-high or 3-high stands without needing a universal mill (which is required for parallel-flange sections like IPE). Learn more about hot rolling mill configurations →

Standards and references

IS 808 : 1989 — Dimensions for hot rolled steel beam, column, channel and angle sections (ISMB profile dimensions, tolerances, and section properties)
IS 2062 : 2011 — Hot rolled medium and high tensile structural steel (material grades E 250 through E 650)
IS 1852 : 1985 — Rolling and cutting tolerances for hot rolled steel products
IS 800 : 2007 — General construction in steel — Code of practice (the design code for all structural steel in India)
IS 1387 : 1993 — General requirements for the supply of metallurgical materials
SP 6 (1) : 1964 — Handbook for structural engineers: Structural steel sections (the original Indian sectional properties handbook)

Related references

ISHB H-Beams — wide flange heavy sections for columns and compression members
ISMC Channels — C-shaped sections for purlins, lateral framing, and built-up members
ISA Angles — L-shaped sections for bracing, trusses, and connections
Rolling Mills: Principles, Components, Processes, and Products — comprehensive technical reference
Hot Rolling Mills Guide — section mills, layouts, configurations

ISMB I-Beams