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Rebar Spacing Calculator — ACI 318 Steel Reinforcement Layout Tool

Calculate Rebar Count, Spacing, Weight, and Coverage for Slabs, Walls, and Footings

Free rebar spacing calculator for concrete contractors, structural engineers, and estimators. Enter the slab or wall dimensions, bar size, and spacing to calculate the number of bars, total linear feet, weight of reinforcement, and steel area per foot of width. Supports standard rebar sizes #3 through #11 and #14/#18 with built-in weight-per-foot and cross-sectional area data.

Covers one-way and two-way reinforcement layouts for slabs on grade, elevated slabs, retaining walls, footings, and grade beams. Includes ACI 318 minimum reinforcement requirements, maximum spacing rules, and clear cover requirements by exposure condition. The material estimator calculates total rebar weight in pounds and tons for procurement.

Pro Tip: For slabs on grade, ACI 318 requires temperature and shrinkage reinforcement of at least 0.0018 x Ag for Grade 60 rebar. For a 6-inch slab, that is 0.13 in2/ft, which is #4 bars at 18-inch spacing or #5 bars at 28-inch spacing. Most contractors default to #4 at 18 inches both ways, which is slightly above minimum and easy to install.

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Concrete Rebar Spacing Calculator
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How It Works

  1. Enter Element Dimensions

    Input the length and width of the slab, wall, or footing. For walls, enter height and length. For footings, enter length, width, and depth. Dimensions in feet and inches or meters.

  2. Select Rebar Size

    Choose the bar size from #3 through #18. The calculator shows the bar diameter, cross-sectional area, and weight per foot for the selected size. Most residential and light commercial work uses #4 or #5 bars.

  3. Enter Spacing

    Specify the center-to-center bar spacing in inches. Common spacings: 6, 8, 12, 16, 18, and 24 inches. The calculator verifies that spacing does not exceed ACI 318 maximum spacing limits (typically 18 inches for slabs or 3 times the slab thickness).

  4. Set Clear Cover

    Enter the required clear cover from the concrete face to the nearest rebar surface. ACI 318 requires: 3/4 inch for interior slabs, 1.5 inches for formed surfaces exposed to weather, 2 inches for concrete cast against earth, 3 inches for concrete exposed to soil or weather with large bars.

  5. Review Results

    See the number of bars in each direction, total linear feet of rebar, total weight in pounds, steel area per foot of width (As), and a comparison to ACI minimum reinforcement requirements. Use the weight for procurement and the bar count for shop drawing verification.

Built For

  • Concrete contractors calculating rebar quantity and weight for slab-on-grade pours
  • Structural engineers verifying that rebar spacing meets ACI 318 minimum reinforcement and maximum spacing requirements
  • Estimators generating rebar takeoffs by weight for bidding and material procurement
  • Residential builders planning rebar layout for footings, grade beams, and basement walls
  • Infrastructure contractors calculating reinforcement for retaining walls and box culverts
  • Inspectors verifying rebar spacing and coverage in the field before concrete placement
  • Engineering students checking ACI 318 reinforcement calculations for coursework

Features & Capabilities

Standard Rebar Sizes #3 through #18

Built-in data for all standard rebar sizes: diameter, cross-sectional area, weight per foot, and perimeter. Covers #3 (0.375 in, 0.376 lb/ft) through #18 (2.257 in, 13.60 lb/ft).

ACI 318 Minimum Reinforcement Check

Verifies that the specified reinforcement meets ACI 318 minimums for temperature/shrinkage steel (0.0018 x Ag for Grade 60), flexural reinforcement (200/fy x bw x d), and maximum spacing limits.

Two-Way Layout

Calculates bar count and weight for both directions in a two-way reinforcement layout. Shows totals for each direction and the combined material weight.

Clear Cover Verification

Checks that the specified clear cover meets ACI 318 requirements based on the exposure condition: interior, formed exterior, cast-against-earth, or exposed-to-weather categories.

Weight and Linear Foot Totals

Outputs total linear feet and total weight in pounds and tons. Includes an adjustable lap splice factor (default 10 percent) to account for splice lengths in the material estimate.

Steel Area per Foot (As/ft)

Calculates the provided steel area per foot of width for comparison against structural drawings and ACI code requirements. This is the value structural engineers specify on plans.

PDF Export

Export a rebar schedule summary as a branded PDF including bar sizes, spacing, count, lengths, and total weight. Suitable for submittals, material orders, and field reference.

Frequently Asked Questions

ACI 318 limits maximum bar spacing to 18 inches or three times the slab thickness, whichever is less, for temperature and shrinkage reinforcement. There is no code minimum spacing, but practical limits are usually 4 to 6 inches minimum to allow concrete placement and consolidation around the bars.
Rebar pricing varies significantly by region and market conditions. As of 2024-2025, Grade 60 rebar in standard sizes runs approximately $700 to $1,200 per ton for material only, with epoxy-coated rebar at a 30-50 percent premium. Contact your local rebar supplier for current pricing.
Building code does not always require reinforcement in a 4-inch slab on grade for non-structural applications (patios, walkways). However, most contractors include #3 or #4 bars at 18-24 inch spacing, or welded wire reinforcement (WWR), to control shrinkage cracking. For structural slabs, vehicle traffic, or expansive soils, reinforcement is required per ACI 318.
ACI 318 requires a minimum Class B tension lap splice of 1.3 times the development length (ld). For #4 Grade 60 bars in normal-weight concrete with 3000 PSI compressive strength, the development length is approximately 24 bar diameters, and the lap splice length is about 31 bar diameters, or roughly 12 inches for #4 bars. Larger bars and higher-strength concrete may require different lengths.
Most residential footings use #4 or #5 bars. A standard 12-inch-wide by 8-inch-deep continuous footing typically has 2 or 3 #4 bars continuous along the bottom with #4 stirrups or dowels at corners and intersections. Local building codes and soil conditions may require more reinforcement. Always follow the structural engineer's specifications or local prescriptive code requirements.
Disclaimer: Rebar calculations are for estimating and planning purposes. Structural reinforcement design must be performed by a licensed structural engineer in accordance with ACI 318 and local building codes. Actual reinforcement requirements depend on loads, soil conditions, and structural analysis.

Learn More

Industrial

ACI 318 Rebar Design Guide: Spacing, Cover, Lap Splices & Minimum Steel

Practical guide to ACI 318 rebar requirements for slabs, walls, footings, and grade beams. Covers temperature steel, maximum spacing, clear cover, lap splice lengths, and common placement mistakes.

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