Global Araç
Rebar Spacing Calculator
Rebar Spacing Calculator
Estimate rebar quantity, tie wire, and cost for a concrete slab. (Beton döşeme için donatı miktarı, bağ teli ve maliyeti hesaplayın.)
Concrete is strong in compression but weak in tension; rebar (reinforcing steel) provides tensile strength. Standard residential applications: slab on grade (driveway, patio, garage floor) uses #3 (3/8 inch) or #4 (1/2 inch) rebar in a 16-inch on-center grid; structural slabs and footings use #4 or #5 (5/8 inch) at 12-inch OC. Spacing matters because concrete sections that crack between rebar can spall; closer spacing = stronger but more material cost. Standard rebar comes in 20-foot sticks; calculate linear feet needed = (slab length × bars-per-row) + (slab width × bars-per-column), divide by 20 to get pieces to buy. Add 40-bar- diameter (40 × 0.5 = 20 inches for #4) lap splice at every joint where two bars overlap — required by ACI 318 building code for tension transfer.
The calculator takes slab dimensions, rebar size (#3 / #4 / #5 / #6), and spacing on center (typically 12, 16, or 18 inches), then outputs: linear feet of rebar needed, pieces (rounded up to next 20-foot stick), tie wire amount (typically 1 lb per 100 ties, with 1 tie per intersection), total material cost. For a typical 12 × 20 ft patio slab with #4 at 16-inch OC: ~75 linear feet × 2 directions = 150 ft total / 20 ft per stick = 8 sticks. At ~$8 per 20-ft #4 stick: $64 in rebar. Plus chairs / dobies (concrete spacers to hold rebar off the ground 1.5-2 inches), tie wire, and bolt cutters / rebar bender for shaping.
Critical considerations: (1) Rebar position matters — for slabs in tension at bottom (typical for slabs with loads above), rebar should be in the bottom 1/3. For slabs in tension at top (cantilevers, retaining walls), rebar in top 1/3. Position with chairs / dobies that hold steel 1.5-2 inches above subgrade. (2) Concrete cover — minimum cover (concrete thickness over rebar) for slabs on grade exposed to weather: 3 inches (top), 1.5 inches (bottom). For protected interior: 1.5 inches all around. Inadequate cover lets moisture reach steel, causing rust and spalling. (3) Lap splices — when joining two bars end-to-end, overlap them by 40 × bar diameter (40 × 0.5 = 20 inches for #4). This transfers tension between bars without weakness at the splice. ACI standard for non-seismic; seismic zones require longer (60×) splices. (4) Wire mesh vs rebar — for thin slabs (under 4 inches), 6×6 W2.9×W2.9 welded wire mesh is acceptable substitute. For slabs 4+ inches with significant loads, rebar is standard. (5) Permits and inspections — structural slabs (footings, foundations) typically require permits and inspection BEFORE pouring; non-structural (patios, driveways) often don't but check local code.
Nasıl Kullanılır
- Enter slab dimensions (length × width in feet).
- Pick rebar size: #3 (3/8 in) / #4 (1/2 in) / #5 (5/8 in) / #6 (3/4 in).
- Pick spacing on center: 12 / 16 / 18 inches.
- Read linear feet, pieces (20-ft sticks), tie wire, total cost.
- Don't forget chairs / dobies for proper rebar elevation off subgrade.
Ne Zaman Kullanılır
- Pouring a residential slab (driveway, patio, garage floor, basement floor).
- Building footings or piers for decks, fences, retaining walls.
- Sidewalk and walkway construction.
- Adding rebar to existing concrete repairs.
- Bulk material purchase planning before delivery.
Ne Zaman Kullanılmaz
- Structural concrete (load-bearing walls, columns, beams) — needs licensed structural engineer.
- Commercial / industrial slabs — needs project-specific engineering.
- Seismic zones requiring special detailing — consult local code and engineer.
- Post-tensioned slabs — different reinforcement system entirely.
Yaygın Kullanım Senaryoları
- Educational use — demonstrating the underlying concept
- Onboarding a colleague who needs the same calculation/conversion
- Verifying a number or output before passing it on
- Quick calculation during a typical workday
Sık Sorulan Sorular
What size rebar should I use?
Residential standards: #3 (3/8 in) for sidewalks and light-duty patios. #4 (1/2 in) for driveways, garage floors, typical slabs on grade — most common residential size. #5 (5/8 in) for footings, foundations, structural slabs. #6 (3/4 in) for heavy footings, retaining walls. Most DIY residential projects use #4 at 16-inch OC; that's the safe default for most slabs.
What spacing should I use?
12-inch OC: heavy-duty applications, footings, slabs with vehicle loads. 16-inch OC: standard residential slabs (driveways, patios, garage floors). 18-inch OC: light-duty (sidewalks, light patios). Closer spacing = stronger but more material. ACI minimum spacing varies by application. When in doubt, 16-inch OC is the safe residential default.
What's a lap splice?
When joining two rebar pieces end-to-end (because rebar comes in 20-ft sticks but slabs are longer), overlap them by 40 × bar diameter — for #4 (0.5 in), that's 20 inches of overlap. ACI 318 building code requirement. Lap splice transfers tension between bars; insufficient overlap creates weakness. Tie the overlapped section with wire to maintain position during pour. Seismic zones require 60× splices.
Wire mesh or rebar?
Wire mesh (6×6 W2.9×W2.9 welded wire fabric): acceptable for thin slabs (under 4 inches), light-duty, no major loads. Cheaper and easier than rebar. Rebar: required for slabs 4+ inches with significant loads (vehicle traffic, heavy equipment). Rebar provides better crack control and structural strength. Most residential driveways and garage floors use rebar; sidewalks and light patios often use wire mesh.
How thick should the slab be?
Standard residential slabs: 4 inches for sidewalks and light patios; 4-5 inches for driveways and garage floors; 6+ inches for heavy-vehicle / commercial applications. Thicker slabs accommodate larger rebar and heavier loads. Pair thickness with appropriate rebar size: 4-inch slab = #4 rebar; 6-inch slab = #4 or #5; 8-inch slab = #5 or #6. Local building code specifies minimums; check before pouring.
Do I need a permit?
Non-structural slabs (patios, sidewalks, decorative concrete): often no permit required, but check local code. Structural concrete (footings, foundations, retaining walls over 4 ft): permits required, with inspection BEFORE pouring (inspector verifies rebar placement and depth). Residential driveways: varies; some jurisdictions require permits over a certain size. Commercial: always permits + engineering. Building without required permit can result in tear-down orders and fines.