The Total Grid Rebar Length calculator computes the total length of rebar needed for one or more mats of rebar in a concrete slab.
INSTRUCTIONS: Choose units and enter the following:
Length of Rebar (LR): 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 is short for "Reinforcement Bars". Rebar is often used inside concrete for added strength, including use in common slabs. This formula provides a length of rebar calculation useful in both calculating the weight of rebar and the cost of rebar. The computes the total length of rebar in a rectangular grid. It employs rebar 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. Lapping is a function of the lapping factor and the diameter of the rebar size.
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 for the rebar lapping length (see below).
The user specified parameters are:
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".
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 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.