Rebar in concrete slab with spacing calculator, to find out how many bars you need for a solid slab in one direction. Several factors must be analyzed, which we will see below.
Average: Rebar in Concrete Slab Estimator
- On average are required, for 10 square meter with 12cm thick slab, 19 strips of 3/8” rods (9ml each one), are 171 ml.
- On average are required, for 100 square feet with 5 inches thick slab, 19 strips of 3/8” rods (30 ft each one), are 570 ft.
- If you want to combine rods of two diameters, there would be 9 rods (of 9ml each one) of 1/2” diameter and 6 rods of 3/8” diameter (of 9ml each one).
How many Rebars You need for a 4m×4m Slab
Using 3/8” Steel Bars in both directions (Mezzanine)
| 4x4m Slab | Quantity of 3/8” Steel Bars (of 9ml) |
|---|---|
| Slab thickness of 10cm | 35.7 strips |
| 12cm thickness | 28.6 strips |
| 15cm thickness | 25.0 strips |
Using 1/2″ (main) and 3/8″ Temperature Steel Bars, on Mezzanine Slab
| 4x4m Slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Rods (of 9ml) |
|---|---|---|
| 10cm thickness | 19.2 steel bars | 8 steel bars |
| 12cm thickness | 14.3 steel bars | 8 strips |
| 15cm thickness | 12.1 steel bars | 8 strips |
Considerations to Calculate How Many Rods for a Slab
The rod quantity values shown take into consideration the following aspects:
How to Calculate the Number of Rods for a Slab?
- Light or distance between supports. It is the free length between supports of the slab. For the calculation of the reinforcement, slabs with a 4m free distance between supports have been considered, for the main steel, regardless of the total area of the slab. Therefore, it can be used, the same for slabs of 3x4m, 4x4m, 4x5m, 4x6m, 4x10m, etc.
The supports can be concrete walls, blocks, bricks, or beams and enclosures. Solid slabs are used for distances (spans) between supports, less than 4.5 to 5 meters.
It has been considered a monolithic slab, cast and supported (“gripped”) by concrete cladding, at least in one sense or direction.
- Uses that the slab will have. If the slab will be a roof or for a mezzanine. A typical use overload has been considered for the mezzanine level of homes, with values between 200 and 250kg/sqm.
In general, the slabs will receive (uniformly) distributed loads.
You can see many 12×12 FEET BEDROOM plans with this measurements, and other interesting ideas for small rooms.
- Slab thickness . The most usual thicknesses have been considered, such as 10cm, 12cm and 15cm, (4 in., 5 in., 6 in.) the last two values being the most used for a housing mezzanine.
For reasons of design, proportions or architectural expression, the concrete slab needs to have a certain thickness. For example, to make the facade look “pretty”.
- How will you load the slab. That is, if the main steel reinforcement of the concrete slab will be in only one direction or in both directions. Calculations have been made to place main reinforcing steel in only one direction, and in addition, temperature steel or distribution perpendicular to the main reinforcement.
- Slab Concrete Strength. For a slab, concrete with a characteristic resistance of 200kg/cm² to 250kg/cm² is recommended. A R’bk=250kg/cm² (25.0MPa) has been considered. Slab concrete must be made with water, cement, sand, and 10 to 19mm gravel.
- Concrete own weight. It is equal to 2400kg/m3.
- Reinforcing Steel Characteristics. Typical steel resistance values are taken, with R’ak=2500kg/cm² and grade A40 steel.
Corrugated steel strips (or rods) with 9 linear meters (30 ft length) each are considered.
- Slab steel coating. Although in areas with aggressive environments or close to the sea it may be higher, 30mm (1 1/4 in.) of net covering of the main mesh is taken as the standard value .
Let’s see different cases that we can present when building, and in each of them, we will know how many rods are used for a slab.
Rebar in Concrete Slab for 20 sqm Slab (215 sq ft)
The calculation to build a 20 sqm slab, using 3/8″ steel bars, both as main reinforcement and for temperature, in the mezzanine slab.
| 20sqm Slab | Quantity of 3/8” Strips (of 9ml) |
|---|---|
| 4 in. thickness | 44.2 steel bars |
| 5 in. thickness | 35.3 steel bars |
| 6 in. thickness | 30.8 steel bars |
Now let’s see how many rods are needed to build a 20 sqm slab, using 1/2” (main) and 3/8” temperature steel bars, in a mezzanine slab.
| 20sqm slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Rods (of 9ml) |
|---|---|---|
| 10cm thickness | 24.0 strips | 10 strips |
| 12cm thickness | 17.8 strips | 10 strips |
| 15cm thickness | 15.1 strips | 10 strips |
It is also important to have the best STEEL BAR WEIGHT CALCULATOR WITH FORMULA.
How many Rods do I need for a Slab of 30 sqm (320 sq ft)
| 30sqm slab | Quantity of 3/8” Strips (of 9ml) |
|---|---|
| 4 in. Thick | 65.3 steel bars |
| 5 in. Thick | 52.0 steel bars |
| 6 in. Thick | 45.3 steel bars |
| 30sqm slab | Qty. of 1/2” Steel bar (of 9ml) | Qty. of 3/8” Strips (of 9ml) |
|---|---|---|
| 10cm thickness | 35.9 strips | 13.5 strips |
| 12cm thickness | 26.7 strips | 13.5 strips |
| 15cm thickness | 22.6 strips | 13.5 strips |
How many Rods do I need for a Slab of 40 square meters
In this case, we could be calculating a 4x10m mezzanine slab, which would help you to build 12×32 ft PLANS OF A HOUSE with one or two floors.
The main steel is placed, saving the free span of 4 meters (13 feet long).
| 40 sqm slab | Quantity of 3/8” Strips (of 9ml) |
|---|---|
| 4 in. Thickness | 86.4 strips |
| 5 in. Thickess | 68.6 strips |
| 5 in. Thickess | 59.7 strips |
| 40 sqm slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Strips (of 9ml) |
|---|---|---|
| With thickness of 10cm | 47.8 strips | 17.4 strips |
| 12cm thickness | 35.6 strips | 17.4 strips |
| 15cm thickness | 30.1 strips | 17.4 strips |
Rebar in Concrete Slab for 50 square meters
You will be able to specify the thickness of the slab, its use (if it is for a roof or for a mezzanine), and other aspects of interest.
| 50 sqm Slab | Quantity of 3/8” Strips (of 9ml) |
|---|---|
| With thickness of 10cm | 107.5 strips |
| 12cm thickness | 85.3 strips |
| 15cm thickness | 74.1 strips |
| 50sqm Slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Strips (of 9ml) |
|---|---|---|
| With thickness of 10cm | 60 strips | 21.3 strips |
| 12cm thickness | 44.5 strips | 21.3 strips |
| 15cm thickness | 37.6 strips | 21.3 strips |
In the case of a 50 square meter slab, I invite you to CALCULATE THE AMOUNT OF RODS FOR A 50 m2 SLAB yourself .
How many Rods do I need for a Slab of 60 square meters
The following calculation would accommodate a 4x15m house, for example.
| 60m² Slab | Number of 3/8” rods (of 9ml) |
|---|---|
| 4 in. thickness | 129 strips |
| 5 in. thickness | 102 strips |
| 6 in. thickness | 88.6 strips |
| 60m² slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Strips (of 9ml) |
|---|---|---|
| With thickness of 10cm | 71.7 strips | 25.2 strips |
| 12cm thickness | 53.4 strips | 25.2 strips |
| 15cm thickness | 45.1 strips | 25.2 strips |
Rebar in Concrete Slab for 70 square meters
| 70 sqm slab | Quantity of 3/8” Strips (of 9ml) |
|---|---|
| With thickness of 10cm | 150 strips |
| 12cm thickness | 119 strips |
| 15cm thickness | 103 strips |
| 70 sqm Slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Strips (of 9ml) |
|---|---|---|
| With thickness of 10cm | 83.7 strips | 29.1 strips |
| 12cm thickness | 62.3 strips | 29.1 strips |
| 15cm thickness | 52.6 strips | 29.1 strips |
To learn more about CALCULATION OF MATERIALS FOR A SLAB, you can continue with this link.
Rebar in Concrete Slab for 80 square meters
| 80 sqm slab | Quantity of 3/8” Strips (of 9ml) |
|---|---|
| 10cm thickness | 170.8 strips |
| 12cm thickness | 135.3 strips |
| 15cm thickness | 117.5 strips |
| 80 sqm slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Strips (of 9ml) |
|---|---|---|
| With thickness of 10cm | 95.6 strips | 33 rods |
| 12cm thickness | 71.2 strips | 33 rods |
| 15cm thickness | 60.1 strips | 33 rods |
Rebar in Concrete Slab for 100 square meters
| 100m² Slab | Qty. of 3/8” Strips (of 9ml) |
|---|---|
| With thickness of 10cm | 213 rods |
| 12cm thickness | 169 rods |
| 15cm thickness | 147 rods |
| 100m² slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Strips (of 9ml) |
|---|---|---|
| 10cm thickness | 120 rods | 41 rods |
| 12cm thickness | 89 rods | 41 rods |
| 15cm thickness | 75.1 rods | 41 rods |
How much Rod do I need for a 1 square meter Slab
If we make a hypothetical calculation, for a solid concrete slab with a 4m free span , to have an average number of steel rods or strips, it would give us the values that appear below.
How many 3/8” Rods do I need for a square meter?
| For 1 sqm of Slab | Qty. of 3/8” Strips (of 9ml) |
|---|---|
| With thickness of 10cm | 2.1 rods |
| 12cm thickness | 1.7 rods |
| 15cm thickness | 1.5 rods |
How many 3/8″ and 1/2″ rods do I need for a square meter?
| For 1m² of slab | Qty. of 1/2” Strips (of 9ml) | Qty. of 3/8” Strips (of 9ml) |
|---|---|---|
| With thickness of 10cm | 1.2 rods | 0.4 rods |
| 12cm thickness | 0.89 rods | 0.4 rods |
| 15cm thickness | 0.75 rods | 0.4 rods |
These calculations of how many rods are needed for a square meter of slab are merely informative.
However, it is useful to have an approximate technical-economic index.
How are Placed the Rods in a Slab?
Rebars are placed in a slab at a specific spacing, to help distribute the weight of the slab and prevent cracking.
The most common pattern is in the form of a grid, with the rods placed at regular intervals.
The spacing between the bars depends on the size of the slab and the type of rebar being used.
The bars are usually placed at the bottom of the slab, but can also be placed at the top of the slab (for example in cantilevered slabs).
The lower placement is more common, since generally, it is about slabs supported at two ends.
The rods are held in place by wire ties or plastic ties.
- Lay out the grid. The first step is to design the grid for the rods. This is done by the plans of structures or construction.
- Use the correct type of rebar. The type of rebar you use depends on the size of the slab and the weight of the load it will support.
- Place the rods. The rods are placed in the lower part of the slab, on mortar blocks, leaving a separation or cover of 30 to 35mm.
- Secure the rods. The rods are secured in place with wire or plastic ties. Tethers should be placed at regular intervals.
- Pour the concrete. Once the rebars are in place, the concrete can be poured. The concrete must be poured slowly and evenly to avoid displacement of the bars.
- Consult with a structural engineer. A structural engineer can help you determine the correct rebar size and spacing for your specific project.
Steel rods are cold bent to the required shape, regardless of diameter.
What Separation Do the Rods Have in a Slab?
The spacing between bars in a slab depends on the size of the slab, the type of rebar being used, and the load the slab will support.
The minimum space between the bars is usually 250mm (10 inches), but this can be reduced to 200mm if the slab is small or if the rebar is larger.
The maximum bar spacing is usually 300mm, but this can be increased if the slab is large or the rebar is smaller.
There are slabs that must be designed with double reinforcing mesh, that is, a mesh, with rods in two directions, below, and another mesh above, also with steel rods in two directions.
Even some mezzanine slabs of houses, which support stairs, or intermediate walls, may require double reinforcing mesh.
There are many variables to consider in establishing the spacing between rebars.
Here is a table of typical bar spacing for different types of slabs:
| Slab Type | Minimum Spacing | Maximum Spacing |
|---|---|---|
| Residential slab | 270mm | 400mm |
| Commercial slab | 220mm | 300mm |
| Industrial slab | 200mm | 250mm |
It is important to consult with a structural engineer or architect to determine the correct space for your specific project.
Here are some additional factors that can affect the spacing between the bars:
- The thickness of the slab. The thicker the slab, the wider the space can be.
- The type of concrete. The stronger the concrete, the wider the rebar spacing can be, although that is also relative.
- The weather. In hot climates, the gap must be wider to allow for thermal expansion.
CONTACT A PROFESSIONAL, for a specific construction project.
If you have any questions, you can write in the comment box.