To determine how much concrete you need, calculate the volume of your project: multiply Length (ft) × Width (ft) × Thickness (inches ÷ 12) to get total cubic feet, then divide by 27 to find cubic yards. For example, a 10x10 ft patio at 4 inches thick requires (10 × 10 × 0.333) ÷ 27 = 1.23 cubic yards. Always add a 10% buffer for spillage and subgrade unevenness.

A standard structural sub-base requires 4 inches (0.333 ft) of compacted crushed stone or gravel (such as #57 gravel or crusher run). To calculate gravel volume: Area (sq ft) × 0.333 ft ÷ 27 = Cubic Yards of gravel. For a 400 sq ft slab (20x20 ft), you will need (400 × 0.333) ÷ 27 = 4.94 cubic yards. In weight, one cubic yard of gravel weighs approximately 1.4 to 1.5 tons, equating to roughly 7 to 7.5 tons of gravel.

Our concrete calculator estimates the exact volume and material quantity for any pour. Simply measure your structure's dimensions, select your shape (rectangular slab, circular pad, tube/column, or stairs), and choose your preferred unit system (Imperial or Metric) to get instantaneous cubic yards, cubic meters, and pre-mixed bag quantities.

The number of concrete bags required depends on your total cubic feet divided by individual bag yield: an 80 lb bag yields 0.60 cu ft (45 bags per cubic yard); a 60 lb bag yields 0.45 cu ft (60 bags per cubic yard); and a 50 lb bag yields 0.375 cu ft (72 bags per cubic yard). Divide your project's cubic footage by the bag yield and add 10% for waste.

To calculate how many bags of concrete you need: first calculate cubic feet (Length in ft × Width in ft × Depth in ft). For a 6x6 ft slab at 4 inches thick: 6 × 6 × 0.333 = 12 cu ft. If using 80 lb bags (0.60 cu ft yield), divide 12 ÷ 0.60 = 20 bags. Adding a 10% margin gives 22 bags of 80 lb concrete.

To find cubic yards of concrete: calculate (Length in feet × Width in feet × Thickness in feet) ÷ 27. For example, a 12x24 ft driveway extension poured 4 inches thick (0.333 ft) is: (12 × 24 × 0.333) ÷ 27 = 3.56 cubic yards. With a 10% safety buffer, order 3.9 to 4.0 cubic yards from the ready-mix supplier.

Concrete mix quantity is based on the volume of the pour. For small-to-medium residential pours, pre-blended dry concrete mix bags contain Portland cement, coarse aggregate, and sand. A typical 100 sq ft slab at 4 inches requires 33.3 cu ft of mix, which equals 56 bags of 80 lb mix, 74 bags of 60 lb mix, or 1.23 cubic yards of ready-mix concrete.

To quickly estimate bags: multiply your project's cubic yards by 45 for 80 lb bags, 60 for 60 lb bags, or 72 for 50 lb bags. For 1.5 cubic yards, you need: 1.5 × 45 = 68 bags of 80 lb mix (or 75 bags including a 10% safety margin).

Square your concrete slab formwork using the 3-4-5 rule (Pythagorean Theorem: a² + b² = c²). Measure 3 feet along one form edge and 4 feet along the adjacent edge; the diagonal distance between the two points must measure exactly 5 feet. For larger slabs, use multiples like 6-8-10 ft or 9-12-15 ft. Finally, measure both corner-to-corner cross diagonals across the full formwork—when both diagonal measurements are identical, your slab is perfectly square.

One cubic yard of concrete equals 27 cubic feet (a block 3 ft long, 3 ft wide, and 3 ft high). Convert all your project dimensions into feet, multiply them together to get cubic feet, and divide by 27 to find exact yards of concrete.

The total concrete needed is determined by calculating the solid geometry of your pour: Slabs use L × W × D ÷ 27; Cylinders and sonotubes use π × Radius² × Depth ÷ 27; Steps calculate individual rise and tread volumes. Always order 10% extra for grade irregularities and formwork expansion.

To find out how much concrete you need, input your slab length, width, and thickness into our live estimator. The tool instantly displays volume in both cubic yards and cubic meters, while calculating exact bag counts for 80 lb, 60 lb, and 50 lb bags.

For residential projects, concrete requirement is based on slab depth: a 4-inch slab needs 1.23 cubic yards per 100 sq ft; a 5-inch slab needs 1.54 cubic yards per 100 sq ft; and a 6-inch slab needs 1.85 cubic yards per 100 sq ft. Multiply your square footage by these factors and add 10% for waste.

Sakrete high-strength concrete mix yields: 80 lb Sakrete bag = 0.60 cu ft (requires 45 bags/cubic yard); 60 lb Sakrete bag = 0.45 cu ft (requires 60 bags/cubic yard); 50 lb Sakrete Fast-Setting bag = 0.375 cu ft (requires 72 bags/cubic yard). Divide your total volume in cubic feet by the bag yield to determine how many Sakrete bags to purchase.

Measure Length (ft) × Width (ft) × Depth (ft) ÷ 27 = Cubic Yards. For example, a 15x15 ft patio at 4 inches (0.333 ft) requires (15 × 15 × 0.333) ÷ 27 = 2.78 cubic yards. Order 3.0 to 3.25 cubic yards from your concrete ready-mix dispatch.

A single cubic yard of concrete requires: 45 bags of 80 lb mix, 60 bags of 60 lb mix, or 72 bags of 50 lb mix. If your calculator result shows 2.5 cubic yards, you will need 2.5 × 45 = 113 bags of 80 lb concrete (or 125 bags with a 10% waste buffer).

Determine your square footage and thickness: for every 10 square feet of a 4-inch slab, you will need approximately 5.6 bags of 80 lb concrete (or 7.4 bags of 60 lb concrete). For 100 sq ft, expect 56 bags (80 lb) plus 6 extra bags for margin.

Calculating a concrete slab takes 5 simple steps: 1. Measure Length and Width in feet. 2. Measure thickness in inches and divide by 12 (e.g., 4 in ÷ 12 = 0.333 ft). 3. Multiply Length × Width × Depth to calculate Cubic Feet. 4. Divide Cubic Feet by 27 to get Cubic Yards. 5. Add 10% extra material for uneven base and spillage.

A 20x20 ft slab (400 sq ft) at a standard 4-inch depth requires 5.0 cubic yards of concrete (approx. 5.5 yards with buffer). Concrete materials alone cost $700–$950. Total installed cost—including site excavation, 4-inch gravel base, formwork, rebar or wire mesh, pouring, and finishing—typically ranges between $2,400 and $4,800 ($6.00 to $12.00 per sq ft), depending on local labor rates and site access.

To calculate Reinforced Cement Concrete (RCC) slab cost, total four major cost components: 1. Concrete volume (M20 or M25 design mix cost per cu yd or m³). 2. Steel reinforcement (typically 80 kg of TMT steel rebar per cubic meter of concrete, or 1.5–2.0 kg/sq ft). 3. Shuttering and formwork centering cost. 4. Labor for bending, placing, pouring, and curing. RCC slabs typically cost $14 to $22 per sq ft (or ₹220 to ₹350 per sq ft in India).

Calculate slab square footage by multiplying Length (ft) × Width (ft). For instance, a 16 ft by 20 ft slab is 320 sq ft. To convert square feet to cubic yards for a 4-inch slab: 320 sq ft × (4 ÷ 12) ÷ 27 = 3.95 cubic yards. For a 6-inch slab: 320 × (6 ÷ 12) ÷ 27 = 5.93 cubic yards.

A 1,000 sq ft slab at 4 inches thick requires 12.35 cubic yards (order 13.5 yards with 10% buffer). Total turnkey cost for a ground-level garage or home slab ranges from $6,000 to $12,000 ($6 to $12 per sq ft) including base prep, rebar, ready-mix concrete, and finishing labor. Elevated RCC structural slabs cost $14,000 to $22,000+ due to heavy engineering and scaffolding.

For a 1,000 sq ft slab: at 4 inches thick, you need 12.35 cubic yards (9.44 m³) of Ready-Mix Concrete (RMC); with 10% waste, order 13.5 cubic yards (approx. 2 truckloads). At 5 inches thick (typical for RCC roof slabs), you need 15.43 cubic yards (11.8 m³); order 17 cubic yards. At 6 inches thick, you need 18.52 cubic yards (14.16 m³).

To calculate Ready-Mix Concrete (RMC) for a slab: Imperial formula: Area (sq ft) × Thickness (ft) ÷ 27 = Cubic Yards of RMC. Metric formula: Area (m²) × Thickness (m) = Cubic Meters (m³) of RMC. Always add a 5% to 10% contingency for pump line holdover, slight formwork deflection, and grade variations.

For a 1,000 sq ft RCC slab at 5-inch thickness using standard M20 grade concrete (ratio 1:1.5:3): the wet volume is 11.8 m³ (dry volume factor 1.54 = 18.17 m³). Cement volume = 1/5.5 × 18.17 = 3.30 m³. At a cement density of 1440 kg/m³, this requires 4,752 kg of cement, which equals exactly 95 to 100 bags of cement (50 kg each). For a 4-inch slab, approximately 76 to 80 bags are required.

A 1,500 sq ft slab at 4 inches thick requires 18.52 cubic yards (14.16 m³) of concrete. Including a 10% safety buffer, order 20.5 cubic yards (delivered in two to three 9-yard concrete mixer trucks). If poured at 6 inches thick for heavy vehicle traffic, you will need 27.78 cubic yards (order 30.5 yards).

For a 1,200 sq ft slab at standard 5-inch RCC thickness with M20 concrete mix (1:1.5:3): the total volume is 500 cubic feet (14.16 m³). Factoring dry volume conversion (1.54 multiplier), you need approximately 115 to 125 bags of cement (50 kg bags), along with 21 metric tons of sand and 38 metric tons of coarse aggregate.

The total cost of an RCC slab includes cement, sand, gravel, TMT steel reinforcement, shuttering/centering rental, and skilled masonry labor. In the US, an engineered RCC slab costs $14 to $22 per square foot. In India and South Asia, RCC roof slab construction ranges between ₹220 and ₹350 per square foot for standard M20 grade concrete with 5-inch thickness.

For a standard 1,200 sq ft residential RCC slab (5 inches thick), steel reinforcement estimation requires roughly 75 kg to 90 kg of TMT steel per cubic meter of concrete, or 1.5 kg to 2.0 kg of steel per square foot of slab area. For 1,200 sq ft, you will need approximately 1,800 kg to 2,400 kg (1.8 to 2.4 metric tons / 3,960 to 5,280 lbs) of steel rebar (typically a balanced mix of 8mm, 10mm, and 12mm TMT bars).