slab - total grid rebar length

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Equation / Last modified by AndrewBudd on 2019/07/23 15:58
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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 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.  

Rebar and Slab Calculators:

General Information

The Total Grid Rebar Length calculator computes the total length of rebar in a rectangular grid.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.


Make sure rebar size (rS), lapping factor (lF) and uncut rebar length (rL) are specified, because they are vital components when accurately computing 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 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