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:
- (L) Length of Slab
- (W) Width of Slab
- (oC) On-center spacing of rebar
- (i) Inset distance from edge of slab to rebar grid
- (m) Number of Mats.
- (rL) Length of the pre-cut rebar
- (rS) Size of Rebar
- (lF) Lapping Factor. 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:
- 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
- Compute the Total Weight of a Slab with Rebar
- Spanish Version: Calculadora de Barras de Refuerzo
The Math / Science
Rebar Grid (one mat) with no lapping 
Rebar Specifications
The Total Grid Rebar Length calculator computes the total length of rebar in a rectangular grid. 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. Lapping is a function of the lapping factor and the diameter of the rebar size.
Lapping
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