The beam size required for a building depends on various factors, including the span of the beam, the load it needs to support, and the structural design. Generally, as the number of stories increases, larger and stronger beams may be needed.

Hi guys in this article we know about beam size calculation formula and beam size for 2 storey, 3 storey, 4 storey & 5 storey building and also know about beam size for 16 ft, 20 ft and 25 foot long span.

**Sizes of beams** are determined on the basis of architectural drawing & designing. If you want to design for residential building structure and where the height of building is not more than 9.5 m and spacing of columns are 4m, you can do it, but it seems little bit smaller section.

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When we draw beam design structure for residential building you have to also check the slenderness ratio, deflection of beam etc. as per I.S. Code guidelines.

**Beam size calculation formula** is depending on Clear span between two column. According to ACI Code rules and guideline span of beam measured in feet then their depth is equal or should be measured in inches. It means if span of beam 16 feet long then their depth should be 16 inches thick.

The size of beam measured in terms of depth and width which is calculated according to IS code 456 2000 rule and guideline, span up to 10 metre long, depth of simply supported beam should be L/20 and width of beam is equal to Depth/1.5, depth of cantilever beam is L/7 and depth of continuous beam is L/26.

**1) Calculation of depth of beam**:- For simply supported beams, L/d = 20, as per IS 456–2000

So, depth d = L/20, if span is 6m long, then depth = 6000mm/20 = 300mm

This should also be not more than 1/4 th of the clear span, as per IS 13920–2016

d= 1/4*6000 = 1500mm

Hence depth can be taken as d = 300mm.

According to ACI code depth of beam is also measured in inches depending on length of a span. Length of span is 16 feet, then their depth should be 16 inches thick.

**2) Calculation of width of beam?** How we calculate and know about width beam, although beam width depending on the structural design but some common Thumb Rule and IS code we describe here, Width/Depth (b/d ratio) of beam should preferably be more than 0.3, as per IS 13920–2016.

So Width/Depth ( b/d) = 0.3

Width = 0.3d = 0.3 × 300 = 90 mm

But width should not be less than 200mm, as per IS 13920–2016

So take width b = 200mm.

**Beam size for 1 storey, 2 Storey, 3 Storey, 4 storey, & 5 storey building**

**Minimum RCC beam size** should not be less than 9″x 9″ (230MM X 230MM), with an additional slab thickness of 125 MM. I generally use a minimum of 4 bars, with 2 bars of 12 MM thickness in the bottom of the beam, and 2 bars of 10 MM at the top of the beam. Steel should be Fe500 Steel with m20 grade of concrete and stirrups of T8@6″C/C. I maintain a concrete cover of 40mm.

The beam size required for a G+0 building need to be 9″×9″, while the beam size required for a G+1 building need to be 9″×12″. Likewise, the beam size required for a G+2 & G+3 building need to be 12″×12″, while the beam size required for a G+4 building need to be 12″×15″. In addition, the beam size required for a G+5 building need to be 12″×18″.

**Beam size for 1 storey (G+0) building**

The standard beam size for a G+0/1-storey residential building is at least 9 × 9 in inches, or 230 × 230 in mm, or 23× 23 in cm, or 0.23 × 0.23 in meter, or 0.75 × 0.75 in feet. So for a one storey building you need 9″× 9″ RCC beam size.

For this general thumb rule, we will assume a structure of G+0 (1 storey or ground floor) residential building, using standard 9″ thick walls, size of an RCC beam should be 9”x 9” (230mm x 230mm) using 4 nos bar, 2 bars of 12mm Fe500 Steel used at bottom and 2 nos of 12mm Fe 500 used at top with m20 grade of concrete and stirrups of T8@6″C/C.

**Beam size for 2 storey (G+1) building**

The standard beam size for a G+1/2-storey residential building is at least 9 × 12 in inches, or 230 × 300 in mm, or 23× 30 in cm, or 0.23 × 0.30 in meter, or 0.75 × 1 in feet. So for a two storey building you need 9″× 12″ RCC beam size.

For this general thumb rule, we will assume a structure of G+1 (2 storey) residential building, using standard 9″ thick walls, size of an RCC beam should be 9”x 12” (230mm x 300mm) using 6 nos bar,4 bars of 12mm Fe500 Steel used at bottom and 2 nos of 10mm Fe 500 used at top with m20 grade of concrete and stirrups of T8@6″C/C.

**Beam size for 3 storey (G+2) building**

The standard beam size for a G+2/3-storey residential building is at least 12 × 12 in inches, or 300 × 300 in mm, or 30 × 30 in cm, or 0.3 × 0.3 in meter, or 1 × 1 in feet. So for a three storey building you need 12″× 12″ RCC beam size.

For this general thumb rule, we will assume a structure of G+2 (3 storey) residential building, using standard 9″ thick walls, size of an RCC beam should be 12”x 12” (300mm x 300mm) using 6 nos bar,4 bars of 12mm Fe500 Steel used at bottom and 2 nos of 12mm Fe 500 used at top with m20 grade of concrete and stirrups of T8@6″C/C.

**Beam size for 4 storey (G+3) building**

The standard beam size for a G+3/4-storey residential building is at least 12 × 12 in inches, or 300 × 300 in mm, or 30 × 30 in cm, or 0.30 × 0.30 in meter, or 1 × 1 in feet. So for a four storey building you need 12″× 12″ RCC beam size.

For this general thumb rule, we will assume a structure of G+3 (4 storey) residential building, using standard 9″ thick walls, size of an RCC beam should be 12”x 12” (300mm x 300mm) using 6 nos bar,4 bars of 12mm Fe500 Steel used at bottom and 2 nos of 12mm Fe 500 used at top with m20 grade of concrete and stirrups of T8@6″C/C.

**Beam size for 5 storey (G+5) building**

The standard beam size for a G+4/5-storey residential building is at least 12 × 18 in inches, or 300 × 450 in mm, or 30 × 45 in cm, or 0.3 × 0.45 in meter, or 1 × 1.5 in feet. So for a five storey building you need 12″× 18″ RCC beam size.

For this general thumb rule, we will assume a structure of G+4 (5 storey) residential building, using standard 9″ thick walls, size of an RCC beam should be 12”x 18” (300mm x 450mm) using 8 nos bar,4 bars of 12mm Fe500 Steel used at bottom and 4 nos of 12mm Fe 500 used at top with m20 grade of concrete and stirrups of T8@6″C/C.

**Beam size for 16 foot span**

Typically in residential buildings, an **RCC beam size** of **12″ × 16″** (or 300 × 400 mm) is required for a 16 foot span. So if the beam span is 16 feet, the depth of the beam should be 16 inches (400mm) thick and the width of the beam should be 16/1.5 = 10.66 inches, say 12 inches (300 mm).

**Beam size for 20 foot span**

Typically in residential buildings, an **RCC beam size** of **12″ × 20″** (or 300 × 500 mm) is required for a 20 foot span. So if the beam span is 20 feet, the depth of the beam should be 20 inches (500mm) thick and the width of the beam should be 20/1.5 = 13.33 inches, say 12 inches (300 mm).

**Conclusions:**

In general, the standard beam size for a G+2/3-storey residential building is at least 12 × 12 in inches, or 300 × 300 in mm, or 30 × 30 in cm, or 0.3 × 0.3 in meter, or 1 × 1 in feet. So for a three storey building you need 12″× 12″ RCC beam size.