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Concrete Rebar Calculator

This concrete rebar calculator estimates the total number of rebar sticks, total linear footage, lap splices, and overall steel reinforcement weight in pounds and kilograms for concrete slabs, driveways, and footings. Enter slab dimensions, bar size (#3 through #8), and grid spacing to get accurate steel takeoffs.

Interactive Rebar Calculator

ENGINEERING SCHEMATIC
Steel Rebar Grid Spacing & Clear Cover
Volume (V) = Area × Depth 1 Cubic Yard = 27 Cubic Feet
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Pro Contractor Recommendation: #4 rebar (1/2" diameter) placed at 12"–18" on-center provides crack control. Maintain minimum 2" concrete cover on bottom and edges using rebar chairs.
Example default values loaded
Slab or Footing Dimensions
Rebar Spacing & Specifications
%
Total Reinforcement Steel Weight
578.0 lbs
(262.2 kg)
Total Linear Steel
865.3 ft
263.8 meters
Stock 20-Foot Bars
44 bars
Order count (20 ft lengths)
Grid Bar Count
40 bars
20 long + 20 cross
Lap Splice Length
15 in
30 × nominal bar diameter

Rebar Size Specifications & Unit Weights

ASTM standard rebar sizes are designated by eighths of an inch. A #4 bar is 4/8" (0.500" diameter). The table below lists standard dimensions and nominal weights per linear foot:

Bar Size Diameter (in) Weight (lb/ft) Nominal Area (sq in) Typical Applications
#30.375" (3/8")0.3760.11Patios, sidewalks, residential crack control
#40.500" (1/2")0.6680.20Standard 4"-6" driveways, garage floors, footings
#50.625" (5/8")1.0430.31Commercial slabs, heavy vehicle pads, retaining walls
#60.750" (3/4")1.5020.44Foundation grade beams, structural columns
#70.875" (7/8")2.0440.60Bridge decks, high-load industrial floors
#81.000" (1")2.6700.79Deep piers, heavy infrastructure foundations

How to Calculate Rebar for a Concrete Slab

To determine rebar quantities for a rectangular two-way reinforcement mat:

  1. Deduct Edge Clear Cover: Concrete expands and contracts, and steel must be protected from soil moisture and air corrosion. ACI 318 recommends 2 inches of clear concrete cover on sides and bottom for ground contact. Subtract 4 inches total from both length and width.
  2. Calculate Bar Runs: Divide net dimension by grid spacing (typically 12" or 18" on-center) and add 1 for the starter bar.
  3. Calculate Total Linear Feet: Multiply the number of bars by their length in each direction, then add standard lap splice length (minimum 30 bar diameters) for runs exceeding standard 20-foot stock bar lengths.
  4. Determine Steel Weight: Multiply total linear footage by the ASTM nominal unit weight of the selected bar size.