Reinforced concrete slabs require the correct amount of rebar for strength and durability. To simplify the process of calculating the required rebar for your slab, we've created this handy Rebar Calculator for Slab.

Inputs Needed

To calculate the required rebar, you'll need the following inputs:

1. Slab Length (L) – The length of your concrete slab.
2. Slab Width (W) – The width of your concrete slab.
3. Horizontal Rebar Spacing (H) – The distance between each horizontal rebar.
4. Vertical Rebar Spacing (V) – The distance between each vertical rebar.
5. Rebar Diameter (D) – The diameter of the rebar used.

Step 1: Calculating the Number of Horizontal and Vertical Rebars

The number of horizontal rebars depends on the width of the slab and the horizontal spacing, while the number of vertical rebars depends on the length of the slab and the vertical spacing.

Formula for Horizontal Rebars:

To find the number of horizontal rebars (Nh):

$Nh=\frac{W}{H}+1$

Where:

• Nh is the number of horizontal rebars,
• W is the slab width,
• H is the horizontal rebar spacing.

Formula for Vertical Rebars:

To find the number of vertical rebars (Nv):

$Nv=\frac{L}{V}+1$

Where:

• Nv is the number of vertical rebars,
• L is the slab length,
• V is the vertical rebar spacing.

Step 2: Calculating the Total Length of Rebars

Next, we calculate the total length of rebar needed. This includes the lengths of both horizontal and vertical rebars.

Formula for Total Horizontal Rebar Length:

The total length of horizontal rebars (Lh) is the number of horizontal rebars multiplied by the length of the slab:

$Lh=Nh\times L$

Where:

• Lh is the total length of horizontal rebars,
• Nh is the number of horizontal rebars,
• L is the slab length.

Formula for Total Vertical Rebar Length:

Similarly, the total length of vertical rebars (Lv) is the number of vertical rebars multiplied by the width of the slab:

$Lv=Nv\times W$

Where:

• Lv is the total length of vertical rebars,
• Nv is the number of vertical rebars,
• W is the slab width.

Formula for Total Rebar Length:

The total rebar length (Lt) is the sum of the total horizontal and vertical rebar lengths:

$Lt=Lh+Lv$

Where:

• Lt is the total rebar length,
• Lh is the total length of horizontal rebars,
• Lv is the total length of vertical rebars.

Step 3: Calculating the Total Weight of Rebars

Finally, to calculate the total weight of the rebar, we need to know the density of steel and the volume of the rebar. Rebar density is typically around 490 lb/ft³ (7850 kg/m³).

Formula for Volume of Rebar:

The volume of rebar is calculated as the total length of the rebar multiplied by its cross-sectional area. The cross-sectional area of the rebar can be calculated using the formula for the area of a circle:

$A=\pi {\left(\frac{D}{2}\right)}^2$

Where:

• A is the cross-sectional area of the rebar,
• D is the diameter of the rebar.

Formula for Total Volume of Rebar:

The total volume of rebar (V) is:

$V=A\times Lt$

Where:

• V is the total volume of rebar,
• A is the cross-sectional area of the rebar,
• Lt is the total rebar length.

Formula for Total Weight of Rebar:

The total weight of the rebar (W) is the volume of the rebar multiplied by the density of steel:

$W=V\times \text{Density}$

Where:

• W is the total weight of the rebar,
• V is the total volume of the rebar,
• Density is the density of steel, typically 490 lb/ft³ (7850 kg/m³).

Conclusion

With these formulas, you can calculate the precise amount of rebar needed for your slab. This ensures you plan your materials accurately, avoiding waste or shortages. Use our Rebar Calculator for Slab to quickly get results by simply inputting your slab dimensions, rebar spacing, and diameter!