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Free concrete calculator for slabs, footings, and pours. Enter length, width, depth to get cubic yards, cubic feet, and bag counts with waste factor.
Size concrete footings from column load and soil bearing capacity. Get minimum footing area, dimensions, and bearing pressure for residential foundations.
Full concrete slab material list: volume, gravel base, vapor barrier, and reinforcement. Plan garage floors, patios, and slabs with complete takeoff quantities.
Divide the span perpendicular to the bars by center-to-center spacing in feet, round down, and add one bar for each edge. This matches ACI typical practice for evenly spaced reinforcement.
Bars = floor(Slab Span ÷ Spacing) + 1Multiply bar count in each direction by the run length in the perpendicular direction, then sum both grids for total rebar length required.
Total LF = (Bars_Width × Slab_Length) + (Bars_Length × Slab_Width)Divide total linear feet by available bar length (typically 20 ft for #4 rebar) and round up. Add lap splice length at joints if bars cannot run full span.
Sticks = ceil(Total LF ÷ Bar Stock Length)Updated: July 2026
A 20×12 ft driveway with #4 rebar at 16″ spacing needs 16 bars in one direction and 10 in the other — about 440 LF total, or 22 sticks of 20 ft bar.
When plans specify #4 @ 18″ OC on a 24×24 ft slab, the calculator confirms 17 bars each way before ordering from the steel supplier.
Higher load or poor soil may require 12″ OC spacing on a 10×10 ft patio — tighter spacing nearly doubles bar count compared to 18″ OC.
Plan reinforcement for concrete slabs, driveways, and footings by calculating how many rebar runs you need at a given on-center spacing. Enter slab dimensions and bar spacing to get bar counts in each direction, total linear feet, and how many standard-length sticks to purchase.