Concrete Rebar Calculator
This rebar calculator lays out a two-way grid for your slab: bar counts each way, total linear feet, lap splice allowance (40 bar diameters) and total steel weight for ordering — real quantities, from real layout math.
Cómo usar esta calculadora
- Introduzca sus dimensiones — pies para longitudes, pulgadas para el espesor.
- Ajuste las opciones — porcentaje de desperdicio, tamaño de la bolsa y el precio local del hormigón.
- Lea sus resultados — el volumen, las bolsas, el peso y el costo se actualizan en vivo mientras escribe.
La fórmula
Bars per direction = floor((span − 2×edge) ÷ spacing) + 1; weight = total length × unit weight (#4 = 0.668 lb/ft); laps = 40 × bar Ø Ejemplo resuelto: A 20 × 10 ft slab, #4 @ 16 in o.c., 3 in edges: 8 bars × 19.5 ft + 15 bars × 9.5 ft = 298.5 lin ft ≈ 200 lb of steel.
A concrete calculator with rebar output answers the yard order: how many sticks, what total footage, what weight. Residential slabs typically run #3 or #4 bars at 12–18 inches on center both ways, sitting on chairs at mid-depth or slightly above.
Lap splices matter once your slab dimension exceeds stock length (20 ft standard): overlap bars 40 diameters (20 inches for #4) and tie. The calculator adds this automatically from your stock length.
Placement beats quantity: bars fully bedded in the middle third of the slab do their job; bars lying on the subgrade do nothing. Use chairs or dobies every 3–4 ft, and keep 3 inches of clearance from edges and 1.5–2 inches of cover from the top surface.
Preguntas frecuentes
Preguntas comunes sobre la concrete rebar calculator.
How much rebar do I need for a slab?
At #4 @ 16 in o.c. both ways, plan on roughly 1.5 linear feet of bar per square foot of slab. This calculator gives the exact count, footage and weight for your dimensions.
What size rebar for a driveway?
#4 (1/2 inch) at 12–16 inches on center is the residential driveway standard; #3 at 12 in suits patios and walks.
How much do rebar laps overlap?
40 bar diameters is the common tension lap: 15 in for #3, 20 in for #4, 25 in for #5. The calculator includes lap footage when bars exceed stock length.
Rebar or wire mesh?
Mesh suits 4-inch patios and walks; rebar grids are better for driveways, thicker slabs and anything structural. Either must sit at proper depth on chairs to work.
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