Calculate the number of rebar pieces, total length, and weight for slabs, footings, and walls.
Step 1: Enter the slab/footing length and width.
Step 2: Set the bar spacing (center to center). Common spacing is 12" (300 mm) for slabs.
Step 3: Select the rebar size. #4 (13M) is common for residential slabs; #5 (16M) for footings.
Step 4: Toggle two-way reinforcement for slabs. One-way is used for strip footings.
The calculator accounts for lap splices where bars need to overlap at joins.
#4 (13M) rebar at 12" (300 mm) spacing is standard for 4" residential slabs. Thicker slabs or higher loads may require #5 (16M) bars or tighter spacing.
The standard lap splice is 40 bar diameters. For #4 bar that's 20" (500 mm). Many codes specify a minimum of 24" (600 mm).
Two-way rebar runs in both directions (a grid) and is used for slabs. One-way rebar runs in one direction only, used for strip footings or walls.