The Rebar in a Circular Shaped Slab calculator estimates the total length and weight of reinforcement bars (rebar) needed for a circular shaped concrete slab. 
INSTRUCTIONS: Choose units and enter the following:
- (r) Radius of Circular Slab (e.g. 12 ft).
- (D) Depth of Slab (e.g. 6")
- (i) Inset from the edge of the circular slab (e.g. 3 inches)
- (oC) on-center spacing of the rebar.
- (rS) Rebar Size
- (LF) Lapping Factor
- (M) Number of rebar mats
- (rL) un-cut Rebar Length
- (WL) Output choice: Choose rebar weight or length
- Details Option
Weight and Length of Rebar in a Circular Slab: The calculator returns the length of rebar in feet, and the weight rebar in pounds. However, these can be automatically converted to compatible units via the pull-down menu. If details are chosen ("YES"), the calculator also returns the following:
- Surface Area of Slab in square feet
- Total Volume of the Slab in cubic yards
- Volume of Concrete in cubic yards
- Concrete Displaced by Rebar in cubic yards
However, these to can be automatically converted to compatible units (e.g. meters or kilograms) via the pull-down menu. 
Circular Slab Calculators
- Cubic Yards of Concrete in a Circular Slab
- Amount of rebar needed in a circular slab
- Surface area of a circular concrete slab
- Perimeter or circumference of a circular concrete slab
- Weight of Concrete in a Circular Slab
Rebar and Slab Calculators:
- Rebar and Concrete in a Slab: The calculator returns all of the following:
- Total Length of rebar in feet
- Total Weight of rebar in pounds
- Total Volume of concrete in cubic yards. Note: this accounts for the concrete displaced by rebar.
- Total Weight of Slab in pounds. Note: this includes the weight of rebar and concrete.
- Length of Rebar in Grid
- Weight of Rebar in Grid
- Rebar in a Wall
- Rebar in an Irregular Shaped Slab
- Rebar in a Circular Slab
- Rebar Lapping Length
- Rebar Cost Estimate
- Weight of Length of Rebar
- Concrete Displaced by Rebar
- Compute the Total Weight of a Slab with Rebar
- Spanish Version: Calculadora de Barras de Refuerzo
Laying Rebar in a Circular Slab
Conventional wisdom says that you lay the first two rebar sticks at 90 degrees through the center of the slab footprint and work outward. A major challenge with rebar in a circular slab is minimizing wasted rebar. When possible, start with the longest cross-section of of your slab and work outwards from there. These will be the longest stretches of rebar in your slab. When you cut off the ends, line them up in a row from shortest to longest. When you get to shorter runs, first see if there is a cut-off section of rebar from your row of cut-offs. This is only a little extra work and will save in both materials and labor removing cut-offs at the end of the project.
General Information
Note1: the default units are feet and inches. However, you can change the input units to metric (SI) or others by clicking on the units selection button (to the right of the entry fields). You can also change the output units to metric (SI) units by clicking on the red output units selection button (to the right of the answer box). In both cases, vCalc will make the automatic conversions.
Note2: The lapping portion of the rebar length calculation assumes that the uncut rebar on site is 40' (feet) in length and that lapping is not necessary under that length. Furthermore, this calculator assumes that rebar is lapped by a factor of 40 times the diameter of the rebar chosen. For the same calculations with the ability to add a different "uncut" length and/or a different lapping factor CLICK HERE.
Rebar Specifications
Usage
Reinforcement bars are often used in concrete including common slabs. This formula provides a length and weigh calculation that is useful in understanding the additional load of the slab added by the rebar steel. It is also useful for calculating the weight of rebar when considering transport. Steel is dense and heavy. Most vehicles would be considerably overloaded in weight of rebar long before their potential volume is full, which poses a significant safety issue. In the U.S., most pickup trucks are rated at a half or three quarters ton load rating. This rating indicates the safe weight of a load that can be carried. The rebar weight formula can help determine how many trips are required to transport the load of reinforcement steel safely.
Lapping
When the dimensions of your slab or wall exceed the length of a single piece of rebar, it is required to lap and tie the rebar to create the added length. There are a few considerations. First, the length of the lap is often specified as 40 times the diameter of the rebar. In this case, 40 is lapping factor. 60 is also a common factor, but the engineering specifications should always be applied. See these YouTube videos to better understand rebar lap:
Second, the typical length of pre-cut rebar is 40' and 60' in the United States.
See Also
- Brick or Block Wall - Number of brick or block needed for a wall.
- Foundation - Poured - Amount of concrete needed for a poured foundation.
- Foundation - Block - Number of blocks needed for a foundation.