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 & Reinforcement 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.