Concrete Slab + Rebar Calculator
Get concrete volume and rebar quantities for any reinforced slab in a single step. Enter slab dimensions, thickness, and rebar spacing — the calculator returns cubic yards of concrete alongside total rebar linear footage, piece count, and weight. Eliminates the need to run the slab and rebar calculators separately.
Slab dimensions diagram
How the Formula Works
Calculate concrete volume
Volume (yd³) = Length × Width × (Thickness ÷ 12) ÷ 27 Length and width in feet, thickness converted from inches to feet
Count rebar rows (bars along width)
Rows = ⌊Length ÷ Spacing⌋ + 1 Count rebar columns (bars along length)
Columns = ⌊Width ÷ Spacing⌋ + 1 Total rebar linear footage (with waste)
Linear ft = (Rows × Width + Columns × Length) × (1 + Waste %) Rebar weight
Weight (lbs) = Linear ft × (Weight per ft) Weight is dynamically calculated based on selected rebar size
Frequently Asked Questions
Every reinforced slab requires both concrete and rebar — calculating them separately from the same dimensions wastes time and creates room for entry errors. This combined calculator uses your slab dimensions once and returns both material quantities in a single step.
12 inches (300 mm) on center is standard for residential slabs, patios, and sidewalks. Use 6–8 inches for driveways and garage floors. Structural engineers specify spacing for load-bearing applications. Closer spacing increases material cost but significantly improves crack resistance.
Yes. Order 5–10% extra concrete for driveways and slabs — running short mid-pour is expensive and causes cold joints. Order 10% extra rebar to account for overlap splices (typically 12–18 inches) and edge cuts.