The Weight of Rebar in a Slab calculator computes the total weight 
Concrete Slab with one Rebar Grid mat of reinforcement bars (rebar) needed for a concrete slab based on the dimensions of the slab and the spacing and size of the rebar.
INSTRUCTIONS: Choose units and enter the following:
- (L) Slab Length
- (W) Slab Width
- (rS) Rebar Size (choose from list)
- (oC) on-center spacing of the rebar (default: 18")
- (i) Inset, distance from the side of the slab to the rebar grid (default: 3").
- (m) Number of Mats
- (OC) The output choice of weight (default) or length.
- (rL) Length of Rebar Sticks (bars being used before they are cut). Common lengths are 20, 30, 40 and 60 feet.
- (LF) Lapping Factor 40 (default) and 60 are common.
Weight of Rebar: The calculator returns the total weight of the rebar in pounds. However, this can be automatically converted into other weight units (e.g. kilograms or tons) via the pull-down menu. If OC set to length, the length of the rebar in the mat(s) is return in feet, which can be automatically converted to other length units (e.g. meters or yards) via the pull-down menu. See the Rebar Calculator for more concrete and rebar functions and features. See VIDEO INSTRUCTION for a YouTube video on the use of this calculator.
The Math / Science
Rebar is short for "Reinforcement Bars". Rebar is often used inside concrete for added strength, including use in common slabs. This formula provides a length and weigh rebar 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 for rebar expense and 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.
The rebar weight algorithm calculates the weight of reinforcement steel bars in a concrete slab. The algorithm calculates the area of the slab, and calculates the length of rebar needed for a rectangular grid within the slab. The grid is specified by the inset from the edge of the slab and the nominal separation between horizontal and vertical rows of rebar (onCenter - see diagram). Once the algorithm calculates the length of rebar, the length is used with the user specified rebar size, and density constants from the vCalc library to calculate the total weight of the reinforcement steel bars.
The user specified parameters are:
- (L) Length - length of the slab
- (W) width - width of the slab
- (rS) size - this is the size of the rebar. The standard sizes include: 2 ,3 ,4 ,5 ,6 ,7 ,8 ,9 ,10 ,11 ,12 ,14, 16, 18, 20
- (oC) OnCenter - the on-center spacing between rebar, which defaults to 18"
- (i) inset - an offset distance from the side of the slab to the first row the rebar grid, which has a default of 3"
- (m) mats - this is the number of mats (layers of grids) of rebar.
- (OC) Output choice - this lets the user choose between the weight of the rebar in the grid or the length of rebar in the grid.
- (rL) Rebar Length - this is the length of the rebar sticks used in constructing the rebar grid.
- (LF) Lapping Factor - this the multiple of the rebar diameter used to define the overlap length at rebar joints (extension).
The calculation determines the need for an extra rebar using an internal tolerance for for a spacing fraction that exceeds the tolerance with a default of 1".
Lapping
Rebar lapping is required when the dimensions of your slab or wall exceed 
the length of a single piece (stick) of rebar. In this case, it is required to lap and tie the rebar to create the added length. There are a few considerations. First, the length of the rebar lap is specified as a factor (LF) times the diameter of the rebar which is different for each size of rebar. Lapping factors of 40 and 60 are common, but the engineering lapping factor specification should always be applied. See the following YouTube videos to better understand rebar lap:
Second, the typical lengths of pre-cut rebar 20', 40' and 60' in the United States.
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
Masonry Calculators
- Total Slab Weight - This includes the weight of the rebar and the concrete.
- 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.