Beams carry slabs and walls to the columns. Their depth governs how much they sag; their width usually follows the wall; their steel decides how much they can carry.
Typical Sizes
| Span | Typical depth (incl. slab) | Typical width |
|---|---|---|
| Up to 3 m | 300 mm | 230 mm |
| 3 – 4.5 m | 300 – 380 mm | 230 mm |
| 4.5 – 6 m | 380 – 450 mm | 230 – 300 mm |
| Over 6 m | 450 mm+ | By design |
Depth includes the slab above; the visible downstand below the ceiling is the beam depth minus the slab thickness.
The Span-to-Depth Rule of Thumb
Depth ≈ span ÷ 12 to span ÷ 15 for typical house beams with ordinary loads. For a 4.0 m span: 270–330 mm, often rounded up to 300–380 mm. IS 456 checks deflection with span-to-effective-depth ratios (basic values 20 for simply supported and 26 for continuous beams, adjusted for steel), and the design checks strength and shear.
Minimum and Typical Steel
| Rule (IS 456) | Requirement |
|---|---|
| Minimum tension steel | 0.85 ÷ fy × b × d (0.17% of b·d for Fe 500) |
| Maximum tension or compression steel | 4% of b × D |
| Stirrup spacing | ≤ 0.75 d and ≤ 300 mm |
| Side face steel | For beams deeper than 750 mm |
Example: a 230 × 380 mm beam with effective depth about 340 mm needs at least 0.0017 × 230 × 340 ≈ 133 mm² — two 10 mm bars (157 mm²) meet the minimum, but most designs use two or three 12 mm bars at the bottom and two at the top to carry the actual loads.
Checks Before Pouring a Beam
- Bottom bars at the right cover, on cover blocks.
- Top bars held up at supports.
- Stirrups at drawn spacing, closer near supports, 135° hooks.
- Laps at the right positions and lengths.
- Formwork true, propped and tight.
- Conduits and sleeves through the beam only where the engineer allows.
The Short Version
A house beam is usually 230 mm wide and about span ÷ 12 to ÷ 15 deep, with steel and stirrups set by the design. Depth is what stops sagging, so never trim it to gain headroom — redesign instead.
