What size should the columns, beams and footings be for a G+1 or G+2 house? This guide gives you the typical sizes used in Indian residential construction, the IS 456 and IS 13920 minimums, a worked example of how a footing is sized from the column load, and a free preliminary size calculator.
Important: these are preliminary sizes for planning, estimating and checking a drawing. The final sizes and reinforcement must come from a structural design by a qualified engineer, especially in seismic zones III, IV and V.
| G+1 column | 230 × 300 mm (zone II); 300 × 300 mm in zones III–V |
|---|---|
| G+2 column | 230 × 380 to 230 × 450 mm (zone II); 300 × 300 to 300 × 450 mm in zones III–V |
| Beam | 230 × 300 to 230 × 450 mm (depth ≈ span ÷ 12) |
| Slab | 125 mm (two-way slab, spans up to about 4 m) |
| Footing (G+1) | about 1.4 × 1.4 m to 1.6 × 1.6 m |
| Footing (G+2) | about 1.7 × 1.7 m to 1.95 × 1.95 m |
Typical sizes for G, G+1, G+2 and G+3 houses
| Building | Column (zone II) | Column (zones III–V) | Beam | Slab | Isolated footing |
|---|---|---|---|---|---|
| G (single storey) | 230 × 300 mm | 300 × 300 mm | 230 × 300 mm | 125 mm | 1.0 – 1.2 m square |
| G+1 | 230 × 300 mm | 300 × 300 mm | 230 × 300 – 380 mm | 125 mm | 1.4 – 1.6 m square |
| G+2 | 230 × 380 – 450 mm | 300 × 300 – 450 mm | 230 × 380 – 450 mm | 125 – 150 mm | 1.7 – 1.95 m square |
| G+3 | 300 × 380 – 450 mm | 300 × 450 mm | 230/300 × 450 mm | 125 – 150 mm | 1.95 – 2.25 m square |
IS code minimums you must not go below
| Member | Requirement | Code |
|---|---|---|
| Column size | IS 456 sets no minimum dimension, but in earthquake-resistant (ductile) design the smallest column dimension must be at least 300 mm and at least 20 × the largest beam bar diameter passing through the joint | IS 13920:2016 |
| Column main steel | 0.8% to 4% of the column area (6% absolute maximum); at least 4 bars in a rectangular column, minimum 12 mm diameter | IS 456 cl. 26.5.3.1 |
| Column ties | Pitch not more than the least column dimension, 16 × the smallest main bar diameter, or 300 mm; closer ties (100 mm or less) near beam–column joints in ductile design | IS 456 cl. 26.5.3.2, IS 13920 |
| Beam size | Width at least 200 mm, width-to-depth ratio more than 0.3, depth not more than ¼ of the clear span | IS 13920:2016 |
| Beam steel | Minimum tension steel As/bd ≥ 0.85/fy | IS 456 cl. 26.5.1.1 |
| Slab steel | Minimum 0.12% of the gross area with HYSD bars | IS 456 cl. 26.5.2.1 |
| Footing | Thickness at the edge at least 150 mm on soil; nominal cover at least 50 mm | IS 456 cl. 34.1.2, 26.4.2.2 |
| Concrete grade | M20 minimum for RCC | IS 456 Table 5 |
Column size for a house
The common “9 × 12 inch” (230 × 300 mm) column became popular because it hides inside a 230 mm brick wall. It is often enough for a G+1 house in seismic zone II with short spans. But most of India is in zone III or higher, and there IS 13920 asks for a minimum dimension of 300 mm. Thin 230 mm columns are also the members most often seen failing in earthquake damage surveys, because they leave little room for confined concrete and proper joint detailing.
A quick preliminary check is to find the column’s area from its factored axial load. For a short column with M20 concrete, Fe500 steel and about 1% steel, the axial capacity per IS 456 cl. 39.3 is roughly 11.3 N per mm² of gross area. Add about 25% for bending in an interior column (more for edge and corner columns):
Required Ag ≈ 1.25 × Pu ÷ 11.3
Beam size for a house
For continuous beams in houses, the overall depth is usually taken as about span ÷ 12 (span ÷ 10 for simply supported or heavily loaded beams), and the width equals the wall thickness, usually 230 mm. The depth includes the slab thickness.
| Beam span (c/c) | Typical size (width × overall depth) |
|---|---|
| 3.0 m | 230 × 300 mm |
| 3.5 m | 230 × 300 – 350 mm |
| 4.0 m | 230 × 350 – 380 mm |
| 4.5 m | 230 × 380 – 400 mm |
| 5.0 m | 230 × 450 mm |
| 6.0 m | 230/300 × 500 mm |
Slab thickness for a house
For two-way slabs with shorter spans up to 3.5 m and normal residential loads, IS 456 cl. 24.1 (Note 2) allows the span-to-overall-depth ratio to be taken as 40 for continuous slabs (35 for simply supported) with mild steel, multiplied by 0.8 for Fe415 steel. That gives about shorter span ÷ 32. In practice most houses use a 125 mm slab; spans above about 4 m need a proper deflection check. See the full method in RCC slab design step by step.
Footing size: how it is calculated
An isolated footing’s plan area comes from the column load and the safe bearing capacity (SBC) of the soil. The service (unfactored) load is used, plus about 10% for the footing’s own weight and the soil above it:
Footing area A = 1.1 × P ÷ SBC → side = √A
A load of 10–12 kN/m² per floor (slab, finishes, walls and live load) is a common preliminary figure for RCC houses. The footing thickness (usually 300–450 mm for houses) and its steel are then decided by bending, one-way shear and punching shear, which is part of the structural design. Footings are usually founded 1.2–1.5 m below ground in normal soil, or deeper where the soil report says so.
Worked example: G+2 house, interior column
- Bay: 3.5 m × 4.0 m, so tributary area = 14 m²
- Load: 12 kN/m² per floor × 3 slab levels (first floor, second floor, roof)
- Column load P = 14 × 12 × 3 = 504 kN (service)
- Footing area = 1.1 × 504 ÷ 150 = 3.70 m², side = 1.92 m → provide 1.95 m × 1.95 m (SBC 150 kN/m²)
- Factored load Pu = 1.5 × 504 = 756 kN; required Ag ≈ 1.25 × 756,000 ÷ 11.3 ≈ 83,600 mm²
- Column: 230 × 380 mm (87,400 mm²) in zone II, or 300 × 300 mm (90,000 mm²) in zones III–V
- Minimum steel at 0.8% of 87,400 mm² = 699 mm² → 4 bars of 16 mm (804 mm²)
- Beam for 4.0 m span: 4,000 ÷ 12 = 333 → 230 × 350 mm (230 × 380 mm is common)
Free preliminary size calculator
Enter the number of floors, the column spacing around an interior column, the soil’s SBC and the seismic zone. The calculator uses the same method as the worked example above.
Typical reinforcement for a G+1 / G+2 house
| Member | Typical main steel | Ties / stirrups / distribution |
|---|---|---|
| Column 230 × 300 / 300 × 300 | 4 nos 12–16 mm (G+1); 4–6 nos 16 mm (G+2) | 8 mm ties @ 150 mm c/c, 100 mm near beams and footing in ductile detailing |
| Beam 230 × 380 | 2 nos 12 mm top, 2–3 nos 12–16 mm bottom | 8 mm two-legged stirrups @ 150 mm c/c, closer (100 mm) near supports |
| Slab 125 mm | 8–10 mm @ 150 mm c/c both ways (two-way) | Top extra bars at continuous edges |
| Footing 1.5–2.0 m | 10–12 mm @ 150 mm c/c both ways at the bottom | Column bars bent into the footing (L-bend) |
Common mistakes on house sites
- Adding a floor later on columns designed for one floor. Check the column and footing for the extra load before planning a future floor.
- Same footing size everywhere. Interior columns carry roughly twice the load of corner columns; footings should reflect that.
- Skipping the soil test. SBC can vary from under 100 kN/m² (soft clay, filled ground) to over 300 kN/m² (dense gravel); footing size changes accordingly.
- Columns not aligned between floors (floating columns) and long cantilevers without design.
- Wide tie spacing near joints, which is where earthquake damage concentrates.
Frequently asked questions
What is the minimum column size for a G+1 house?
230 × 300 mm is commonly used in seismic zone II with short spans. In zones III, IV and V, IS 13920:2016 requires the smallest column dimension to be at least 300 mm, so 300 × 300 mm is the practical minimum.
Is a 9 inch column enough for a G+2 house?
A 230 mm (9 inch) wide column can work for G+2 in zone II if it is deep enough (230 × 380 to 230 × 450 mm) and designed for the load. In zones III–V, use at least 300 mm in both directions.
What is the footing size for a G+1 house?
For an interior column with a 3.5 × 4 m bay on soil with SBC 150–200 kN/m², about 1.4 × 1.4 m to 1.6 × 1.6 m. Weaker soil or bigger bays need larger footings.
How deep should the footing be for a house?
In normal soil, house footings are usually founded 1.2–1.5 m below ground level, on firm undisturbed soil. Black cotton soil, filled ground and sloping sites often need deeper or different foundations, as decided from the soil report.
What beam size is used for a 4 m span?
Usually 230 × 350 mm to 230 × 380 mm overall depth (including the slab), based on the span ÷ 12 rule for continuous beams.
Related guides
- House Construction Cost in India 2026
- Safe Bearing Capacity of Soil: Values Table & Formula
- Pad Footing: Meaning, Use & Design
- Types of Columns in Construction
- Clear Cover in RCC as per IS 456
References: IS 456:2000 (Plain and Reinforced Concrete), IS 13920:2016 (Ductile Design and Detailing of RC Structures) and IS 875 (Part 1 & 2) for loads. Sizes here are for preliminary planning only.
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