ISMB Beam Size Chart: Dimensions, Weight Per Meter & IS 808 Standard Guide
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Introduction
When it comes to load-bearing structural steel, ISMB beams (Indian Standard Medium Weight Beams) are the go-to choice for engineers, contractors, and fabricators across India. Whether you’re designing a building frame, an industrial shed, or a bridge component, knowing how to read an ISMB size chart correctly is essential for both structural accuracy and cost estimation.
This guide covers what ISMB beams are, how their standard sizing works under IS 808, and how to interpret weight-per-meter data for your project.
What Is an ISMB Beam?
ISMB stands for Indian Standard Medium Weight Beam, an I-shaped (or H-shaped) hot-rolled steel section manufactured to IS 808:1989 specifications. The “I” profile — a central web with flanges on top and bottom — makes these beams highly efficient at resisting bending loads, which is why they’re a primary choice for structural framing.
ISMB beams are used in:
- Multi-storey building columns and beams
- Industrial shed and warehouse framing
- Bridge girders and overhead structures
- Crane runway beams
- Heavy machinery support structures
Like channels, ISMB sizes are designated by a number that approximates the depth of the beam in millimetres — for example, ISMB 100, ISMB 200, ISMB 300, up to ISMB 600.
How to Read an ISMB Size Chart
A typical ISMB chart includes the following columns:
| Parameter | Description |
|---|---|
| Designation | Nominal size, e.g., ISMB 150, ISMB 250 |
| Depth (h) | Overall height of the beam (mm) |
| Flange Width (b) | Width of top and bottom flanges (mm) |
| Web Thickness (tw) | Thickness of the central web (mm) |
| Flange Thickness (tf) | Thickness of the flanges (mm) |
| Sectional Area | Cross-sectional area (cm²) |
| Weight per Meter | Mass per running meter (kg/m) |
| Moment of Inertia (Ixx, Iyy) | Bending resistance values used in design |
Sample ISMB Weight Chart (Common Sizes)
| Designation | Depth (mm) | Flange Width (mm) | Approx. Weight (kg/m) |
|---|---|---|---|
| ISMB 100 | 100 | 75 | ~11.5 |
| ISMB 125 | 125 | 75 | ~13.0 |
| ISMB 150 | 150 | 80 | ~14.9 |
| ISMB 200 | 200 | 100 | ~25.4 |
| ISMB 250 | 250 | 125 | ~37.3 |
| ISMB 300 | 300 | 140 | ~44.2 |
| ISMB 400 | 400 | 140 | ~61.6 |
| ISMB 600 | 600 | 210 | ~122.6 |
Note: These are indicative reference figures. Always confirm exact values against the latest IS 808 tables or your mill’s test certificate before finalizing structural design or procurement quantities.
How ISMB Weight Is Calculated
Like all hot-rolled steel sections, ISMB weight per meter is derived from the beam’s cross-sectional area multiplied by steel density:
Weight (kg/m) = Cross-sectional Area (cm²) × 7.85
This is why two beams with the same depth but different flange widths or web thicknesses can have noticeably different weight-per-meter values — the sectional area, not just the outer profile, drives the number.
ISMB vs ISMC vs ISA: Know the Difference
It’s common for buyers to confuse these three structural sections:
- ISMB (Beam) — I-shaped, optimized for bending resistance; used as primary load-bearing members.
- ISMC (Channel) — C-shaped, often used for secondary framing, purlins, and bracing.
- ISA (Angle) — L-shaped, used for bracing, brackets, and lighter connections.
Using the wrong chart for your section type is one of the most common (and costly) estimation errors in steel procurement.
Why Accurate ISMB Weight Data Matters
- Structural design compliance — engineers rely on precise Ixx/Iyy and weight values for load calculations; approximations aren’t acceptable at the design stage.
- Accurate project costing — beams are priced per kg or tonne, so incorrect weight assumptions can significantly distort budgets on large structural orders.
- Transport and crane planning — beam weight determines how loads are split across trucks and what lifting equipment is required on site.
- Delivery verification — comparing theoretical weight per meter against delivered tonnage helps confirm you’ve received the correct quantity and grade.
Frequently Asked Questions
1. What does ISMB stand for? ISMB stands for Indian Standard Medium Weight Beam, an I-shaped structural steel section manufactured under IS 808:1989 and used primarily as a load-bearing member.
2. How is ISMB different from ISMC? ISMB beams have an I-shaped profile optimized for bending resistance and are used as primary structural members, while ISMC channels have a C-shaped profile typically used for secondary framing, purlins, and bracing.
3. How do I estimate the total tonnage of ISMB beams needed for a project? Multiply the weight per meter (kg/m) for your chosen designation by the total running length required, then sum across all beam sizes used in the project to get the total tonnage.
4. Why do two ISMB beams with the same depth have different weights? Weight per meter is based on cross-sectional area, not just depth. Differences in flange width, web thickness, or flange thickness between beam variants of the same depth will result in different weight-per-meter values.
Conclusion
The ISMB size chart is a foundational reference for anyone working with structural steel in India. Understanding how depth, flange width, and sectional area translate into weight per meter — and cross-checking that against IS 808 — ensures your structural design, costing, and procurement all stay accurate and compliant.
For verified ISMB specifications, live stock availability, and mill test certificates, visit our [Structural Steel Products] page for complete size-wise details.
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A: Carbon steel relies on carbon content alone for its properties. Alloy steel adds elements like chromium, nickel, molybdenum, and vanadium to achieve specific improvements — higher strength, better low-temperature toughness, creep resistance, or corrosion resistance — giving it a far broader performance range than carbon steel.
A: For ambient to 400°C service, ASTM A516 Grade 70 is the standard choice. For high-temperature refinery or power plant use (up to 600°C), ASTM A387 Grade 11 or 22 (chrome-moly) applies. For cryogenic service down to -196°C, 9% nickel steel (ASTM A553) is required.
A: Wear-resistant grades like AR400/AR500 are quenched to martensitic hardness of 370–500 HB — 3–4× harder than structural grades like A572-50. They resist abrasive wear in mining and construction equipment but have limited weldability and are not suitable as primary structural members.
A: CE (= C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15) predicts susceptibility to hydrogen-induced cold cracking during welding. Sheets with CE above ~0.40 require preheating to slow cooling and allow hydrogen diffusion, preventing weld cracking. Always develop a qualified WPS based on the specific CE value.
