Rebar Calculator — Length, Weight & Spacing
Calculate reinforcing steel (rebar) requirements for concrete slabs, walls, footings, and columns. Determine bar count based on spacing, total weight for ordering, and lap splice requirements per ACI 318.
Why This Construction Metric Matters
Why: Rebar transforms brittle concrete into a ductile, crack-resistant structural system. Under-specifying rebar leads to structural failure; over-specifying wastes money on expensive steel. Proper spacing, lap splice lengths, and concrete cover are code requirements that must be met for inspection approval.
How: For slabs: divide each dimension by bar spacing and add 1 for each direction. Calculate total bar length, add lap splice length at each joint (typically 40× bar diameter). Multiply total length by weight per foot for ordering. Check minimum cover (1.5 in for interior slabs, 3 in for footings).
- ●ACI 318 requires minimum rebar cover of 1.5 inches for interior slabs and 3 inches for footings exposed to soil.
- ●#4 bars at 12 inches on center is the most common slab reinforcement for residential construction.
- ●Rebar should be tied at every other intersection—tying every intersection wastes time without structural benefit.
- ●Epoxy-coated rebar costs 15-25% more but is required in corrosive environments (coastal, parking garages).
Rebar Calculator
Quantity • Weight • Spacing • Lap Splice • Cost
Quick Examples — Click to Load
Garage Slab
20×24 ft, 4" thick, #4 @ 12"
Patio Slab
16×12 ft, 4" thick, #3 @ 18"
Foundation Footing
80 ft perimeter, 24" wide, #5 @ 8"
Driveway
60×12 ft, 6" thick, #4 @ 12"
Concrete Beam
20 ft beam, 12×24", 4-#6 bars
Basement Slab
40×30 ft, 6" thick, #5 @ 10"
Pool Deck
50×20 ft deck, 5" thick
Custom Project
Enter your own specifications
📐 Calculation Mode
#4 (13M)
📏 Dimensions
📐 Spacing & Cover
Planning estimates only. Verify with a licensed engineer or contractor before construction.
📐 Construction Industry Facts
The US uses approximately 10 million tons of reinforcing steel annually in concrete construction.
— CRSI 2024
Grade 60 rebar (60,000 PSI yield strength) is the standard—Grade 80 is emerging for high-performance applications.
— ACI 318-19
Standard rebar comes in 20-foot and 60-foot lengths; #3 through #11 are standard sizes.
— CRSI
Over 70% of rebar is made from recycled steel, making it one of the most sustainable construction materials.
— Steel Recycling Institute
What is a Rebar Calculator?
Determines quantity, weight, and spacing of reinforcing steel for concrete. Rebar adds tensile strength.
Bar Count
Bars needed
Weight
Total tonnage
Sizes
#3–#18
Lap Splices
Overlap
How to Calculate
When to Use
Slabs, footings, beams, columns, walls.
Why It Matters
Structural integrity, tensile strength for concrete.
Where Applied
Foundations, slabs, retaining walls, structural concrete.
Formulas
N = L/s + 1. W = N × L × w_per_ft. Lap = 30–50× diameter.
Tips
- • Add 5–10% for waste and lap
- • #4 typical for slabs; #5–#6 for footings
Common Mistakes
- • Wrong spacing (12" vs 18")
- • Forgetting lap splice length
FAQs
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