What This Calculator Does
The rebar calculator estimates the amount of reinforcing steel bar needed for a rectangular concrete slab laid out in a simple perpendicular grid, based on the slab’s dimensions and your chosen bar spacing.
How the Calculation Works
The number of bars running in each direction is found by dividing the slab’s width or length by the grid spacing (plus one extra bar for the starting edge). Multiplying each direction’s bar count by the length of the perpendicular span gives the total linear footage, and a splice overlap allowance is added per bar to account for how bars are lapped together at their ends. Total weight is calculated using the standard weight-per-foot for the rebar size selected, and the grid intersections figure estimates how many tie-wire points the grid will have.
Tips for Rebar Placement
- Common residential slab spacing is 12 to 18 inches on center; check local code and engineering specs for your project.
- Rebar should typically be supported on chairs to sit at the correct height within the slab, not resting directly on the ground.
- Always round up bar purchases to standard stock lengths (commonly 20 or 40 feet) and add extra for cutting waste.
Note: This is a general planning estimate only. Structural reinforcement requirements should always be confirmed with a licensed engineer and local building code before construction.