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Calcimator

Rebar Spacing Calculator

Calculate rebar spacing, bars per foot, and steel ratio for concrete slabs. Checks ACI code compliance for maximum spacing.

Inputs

in

ACI 318: one-way slab minimum L/20 (simple) to L/28 (one end continuous); 4–8" typical

in

ACI 318 Table 20.6.1.3: slabs not exposed 1.5"; footings in soil 3"; exposed to weather 2"

in²/ft

Results

Bar Spacing

7.74 in

≈ 2 credit cards

ACI Code Compliant

1

Bars per Foot1.55
Steel Ratio0.61%
Effective Depth4.25 in
Max Allowed Spacing18 in
How to Use This Calculator
  1. Enter slab thickness (inches) and select rebar size (#3 through #10).
  2. Set required steel area (in²/ft) from your structural design.
  3. Review maximum allowable spacing (inches) and actual provided steel area.
  4. Spacing must not exceed 3× the slab thickness or 18 inches per ACI 318.

How the result changes with Required Steel Area

Required Steel AreaBar SpacingACI Code Compliant
1.012.38 in1
3.510.68 in1
6.50.37 in1
90.27 in1

What each input means

Slab Thickness
Total thickness of the concrete slab. ACI 318 Table 7.3.1.1 specifies minimum slab thicknesses based on span. Typical one-way slabs: 4–8 inches; two-way slabs: 5–12 inches.
Rebar Size
Standard rebar size number. #4 and #5 are most common for slabs; #8+ for beams and columns.
Concrete Cover
Minimum clear cover over rebar per ACI 318 Table 20.6.1.3. Cast-in-place: slabs 1.5" (not exposed), beams 1.5"–2", columns 1.5", footings in contact with soil 3", exposed to weather 2" (#6 and larger).
Required Steel Area
Required area of steel per linear foot of slab width, from structural design calculations.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Slab Thickness = 6, Rebar Size = 4, Concrete Cover = 1.5, Required Steel Area = 0.31 = 4 input(s) provided
  2. Calculate Bar Spacing
    Bar Spacing
    7.74 = 7.74
  3. Calculate ACI Code Compliant
    ACI Code Compliant
    1 = 1
  4. Calculate Bars per Foot
    Bars per Foot
    1.55 = 1.55
  5. Calculate Steel Ratio
    Steel Ratio
    0.61 = 0.61

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