slab - total grid rebar length

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Equation / Last modified by AndrewBudd on 2018/01/19 21:02
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KurtHeckman.slab - total grid rebar length

The Total Grid Rebar Length calculator computes theslab 1.png total length of rebar needed for one or more mats of rebar in a concrete slab.

INSTRUCTIONS: Choose your preferred units and enter the following:

  • (L) The length of the slab
  • (W) The width of the slab 
  • (oC) The on-center spacing of the rebar spacing (defaults 18")  
  • (i) The inset distance from the side of the slab to the rebar grid (default of 3").
  • (m) The number of mats.  (default is one).
  • (rL) The length of the pre-cut reinforcement bars being used to determine if lapping is required.
  • (rS) The size of rebar  which is used to compute the diameter for lapping considerations.
  • (lF)  The lapping factor is the multiple of the diameter of the rebar to specify the lapping distance.  40 (default) and 60 are common.

Length of Rebar: The calculator returns the length of rebar in feet.   However, this can be automatically converted into other length units (e.g. meters or yards) via the pull-down menu.  

Related Calculators:

  • To compute the Weight of Rabar in a slab, CLICK HERE.
  • To compute the Surface Area of a slab, CLICK HERE.
  • To compute the Surface Area of Concrete Forms, CLICK HERE.
  • To compute the Volume of Concrete in a slab, CLICK HERE.
  • To compute the Weight of Concrete in a slab or wall, CLICK HERE.
  • To compute the Total Weight of a Slab with Rebar, [Could not locate page KurtHeckman.slab – total weight estimate].

General Information

This calculator computes the length of a simple rectangular grid of rebar.slabtotalgridrebarlength-illustration.png                   Rebar Grid (one mat) with no lapping  RebarSpec.jpg Rebar Specifications   It employs lapping for dimensions (length or width) in excess of the user specified rebar lengths (rL: see Lapping below).  A tolerance for determining the need for an extra rebar is set to less than one inch  for a spacing fraction above the tolerance.


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 them 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 rebar is 40' and 60' in the United States.

See how much the rebar will weigh - Rebar Weight