Rebar Calculator

Not Reviewed
Calculator / Last modified by AndrewBudd on 2018/01/19 21:07
Length of Rebar in Grid
Weight of Rebar in Grid
Rebar in a Wall
Rebar in Irregular Shaped Slab
Rebar in Circular Slab
Rebar Lapping Length
Rebar Cost Estimate
Weight of Length of Rebar

The Rebar Calculator contains equations and data used in working with reinforcement bars (rebar) in concrete slabs.  The formulas calculate materials needed for rectangular, circular and irregular shaped slabs.  slabRebar.png(para español, HAGA CLIC AQUÍ) .

Reinforcement Bar (rebar) Functions

  • Length of Rebar in GridInchFracDec.png
  • 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

Rebar Function Details

  • Length of Rebar in Grid:  The user enters the dimensions of the slab (Length and Width), the onCenter spacing of the rebar and the inset from the edge of the slab for the rebar grid.   The user can also enter lapping factors: length of uncut rebar, rebar size and a lapping factor. The formula returns the total length of rebar needed to build such a grid  (see diagram above).Irregular Rebar.pngRebar in Irregular Shaped slab.Rebar Circular Slab.png
  • Weight of Rebar in Grid: The user enters the dimensions of the slab as in the Length of Rebar in a Grid formula (above), and selects a size of rebar (see table).  The formula calculates the total length needed for the grid and applies the weight measurement for the specified rebar size to provide the Total Weight of the Rebar Grid.
  • Rebar in a Wall:  This lets the user enter the dimensions of a wall and rebar specifications and computes the length and weight of rebar, the volume of concrete, and/or the surface area of the forms for a concrete wall.
  • Rebar in an Irregular Slab:  This function computes the length and/or weight of rebar in an irregular shaped slab based on the spacing and the rough area and perimeter of the slab.
  • Rebar in a Circular Slab:  This computes the length and/or weight of rebar in a circular slab based on the spacing and the radius of the slab.
  • Rebar Lapping Length (New): This computes the length of rebar lapping based on the size of rebar and a lapping factor.  The size is used to set the rebar diameter.RebarSpec.jpg Rebar Specifications 
  • Rebar Cost Estimate (New):  This computes the estimated cost of rebar based on the total length of rebar, the length of the pieces (rebar sticks) and the per piece (stick) price.
  • Weight of a Length of Rebar: This lets the user enter any length and select a size of rebar.  It then returns the weight of that length of rebar.

Related Items:


BNT-40_2016-768x768.jpgBN Products BNT-40 Rebar TierRebar Lapping.png

When the dimensions of your slab or wall exceed the length of a single piece of rebar, it is required to lap and tie rebar pieces to create the added length.  This is called Lapping, and the length of the overlapping rebar is the Lapping Length.  There are a few considerations.  First, the length of the lap is specified by a "Lapping Factor (LF)" which is often 40 times the diameter of the rebar. 60 is also a common factor, but the engineering specifications should always be applied.  See these YouTube videos to better understand rebar lap:

The typical length of pre-cut rebar is 40' and 60' in the United States.  


The Rebar in a Wall function also computes the size of the forms.  Concrete forms are a vital part of construction.  The Form Area of Concrete Wall function in this calculator helps compute the amount of plywood or OSB needed to construct the forms.   It give you the choice of specifying whether you want to compute:

  • One Side:  This is just the face of one side of the form.
  • Two Sides: This is the face of both sides of the form.
  • Two Sides and Edges:  This is the most common amount of plywood needed to build a form.  It entirely encloses the volume to be poured.        Plywood Forms for ConcreteForms.png


The term rebar is short for reinforcement bars, and refers to bars of steel embedded in concrete to improve tensile strength.

Rebar Calc in Spanish

The Rebar Calculator is now available in Spanish.  It has Spanish language descriptions, labels and diagrams and it also has default units in the metric system (SI).  The lengths are in meters and centimeters, the areas are in square meters, the volumes are in cubic meters, and the weights are in kilograms and metric tons.

Calculadora de Barras de Refuerzo