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Concrete calculator for slabs, columns, footings, curb and stairs. Get cubic yards, m3, 60/80 lb bag counts and the M20 mix ratio take-off.
The Concrete Calculator estimates the volume and weight of concrete necessary to cover a given area. Purchasing slightly more concrete than the estimated result can reduce the probability of having insufficient concrete.
Mix Design Take-off
Select a mix to get cement, sand, aggregate and water quantities. Dry quantities use the 1.54 bulking factor; verify against your specification before ordering.
Slabs, Square Footings, or Walls
Hole, Column, or Round Footings
Circular Slab or Tube
Curb and Gutter Barrier
Stairs
Have feedback? Report bugs, suggest features, or share your thoughts — we read them allWhat is a Concrete Calculator?
A Concrete Calculator is an essential construction tool that helps estimate the volume and weight of concrete needed for various structural elements. It supports multiple shapes including rectangular slabs, cylindrical columns, and hollow tubes. By entering dimensions and quantities, you can quickly determine material requirements, reducing waste and ensuring you order the correct amount of concrete for your project.
Types of Concrete Shapes
- Slabs, Footings, and Walls (Rectangular): Used for flat surfaces like floors, walls, foundations, and square footings. Volume is calculated as length × width × thickness.
- Columns and Round Footings (Cylindrical): Used for circular columns, round footings, and holes. Volume is calculated using the cylinder formula: π × radius² × height.
- Tubes and Circular Slabs (Hollow Cylinder): Used for hollow structures like tubes, pipes, and circular slabs with holes. Volume is calculated as π × (outer radius² - inner radius²) × height.
- Curb and Gutter Barriers: Used for roadside curbs with gutter channels. Volume is calculated by adding the curb rectangular section and the gutter flat section: (curb depth × curb height + gutter width × flag thickness) × length.
- Stairs: Used for concrete stairways. Volume is calculated by summing the individual step volumes plus the platform: each step increases in volume, creating a stepped structure.
Volume Formulas
Rectangular Slab:
V = L × W × H
Cylinder (Column):
V = π × r² × h
Hollow Cylinder (Tube):
V = π × (R² - r²) × h
Curb and Gutter:
V = [(CD × CH) + (GW × FT)] × L
Stairs (solid pour):
V = run × rise × W × (1 + 2 + … + n) + (PD × W × run)
Mix Design (dry quantities):
Dry = V × 1.54 ; Cement = Dry × (part / Σparts) × 1440 kg/m³
Tips for Using Concrete Calculator
- Always add 5-10% extra concrete to account for spillage, uneven ground, and over-excavation
- Ensure all measurements are in the same unit or use the unit converter provided
- For irregular shapes, break them down into multiple simple shapes and calculate separately
- Standard concrete density is approximately 2,400 kg/m³ (150 lb/ft³)
- Round up to the nearest bag or cubic yard when ordering concrete
- Consider weather conditions - concrete sets differently in hot vs. cold weather
- Always verify measurements on-site before ordering concrete
About Concrete
Concrete is a composite material consisting of coarse aggregates (sand, gravel, crushed stone) bonded together with cement and water. Portland cement is the most common type used in construction. The concrete mixture must be placed before it hardens, typically within 90 minutes of mixing. Proper curing is essential - concrete reaches over 90% of its final strength in about 28 days. Common applications include foundations, slabs, walls, columns, driveways, and structural elements in buildings and infrastructure.
Frequently Asked Questions
Multiply length × width × thickness in consistent units, then convert to the unit your supplier uses — cubic yards in the US, cubic meters everywhere else. For a 10 ft × 12 ft slab at 4 inches thick: 10 × 12 × (4/12) = 40 ft³, divided by 27 = 1.48 yd³. For a circular column, use π × r² × height. For irregular shapes, break the area into rectangles and circles and sum them. Always add a waste allowance of 5-10% for spillage, uneven subgrade, and overpour at edges; bump to 15% for hand-mixed bags. This calculator handles slabs, columns, footings, and tubes with automatic conversion between m³, yd³, and ft³.
Concrete volume = area × thickness for slabs, π × r² × height for columns and round footings, and (π × r₁² − π × r₂²) × height for hollow tubes or sonotubes. Keep every dimension in the same unit before multiplying or your answer will be off by a factor of 12 or more. The most common mistake is mixing feet and inches: a 4-inch slab is 0.333 ft thick, not 4 ft. The result is always a volume — multiply by 150 lb/ft³ (or 2,400 kg/m³ for normal-weight concrete) if you also need the weight for transport or load calculations.
A standard 80 lb bag of pre-mixed concrete yields about 0.60 ft³ once mixed with water, so one cubic yard (27 ft³) takes roughly 45 bags. A 60 lb bag yields 0.45 ft³ — 60 bags per cubic yard. A 40 lb bag yields 0.30 ft³ — 90 bags per cubic yard. Bag mixes are economical up to about 0.5 yd³ (≈ 22 bags of 80 lb), after which ready-mix delivery is cheaper, faster, and stronger because of consistent water-to-cement ratio. For any pour over 1 yd³, call a ready-mix truck and order to the nearest 0.25 yd³ above your calculated volume.
1 cubic yard equals 0.7646 cubic meters, and 1 cubic meter equals 1.308 cubic yards. North American ready-mix suppliers price by the cubic yard; the rest of the world uses the cubic meter. A typical concrete truck holds 10 yd³ (about 7.65 m³). If your supplier requires metric and you measured in feet, convert dimensions first or multiply your cubic-yard result by 0.7646. This calculator displays both units side by side so you don't have to remember the factor when crossing borders or reading manufacturer specs from different regions.
For light foot traffic (patios, walkways, shed floors), 4 inches (10 cm) is standard. For a residential driveway carrying a car or light SUV, use 4 inches with #4 rebar on 18-inch centers; bump to 5 inches (12.7 cm) for occasional truck use. For a garage floor, 4-6 inches is typical. For a heavy-duty driveway or RV pad, go to 6 inches (15 cm) with rebar. Commercial slabs supporting forklifts run 6-8 inches. Always add a 4-inch compacted gravel base under any slab, and a vapor barrier under interior slabs in cold climates. Joints every 10-12 feet control cracking.
Standard concrete (with normal-weight aggregate) weighs about 150 lb per cubic foot, 4,050 lb per cubic yard, or 2,400 kg per cubic meter when freshly placed. Lightweight concrete (with shale or expanded-clay aggregate) drops to 90-120 lb/ft³ (1,440-1,920 kg/m³). High-density concrete using barite or magnetite aggregate can exceed 240 lb/ft³ (3,850 kg/m³) for radiation shielding. The weight matters for transport (a 10 yd³ truck weighs about 66,000 lb gross), for formwork pressure during the pour, and for structural load on framing. This calculator outputs weight automatically using the 150 lb/ft³ standard.
Concrete reaches about 70% of its design strength in 7 days and 90% in 28 days under good conditions (50-90°F, kept moist). For a residential driveway with 4,000 psi mix, wait at least 24 hours before walking, 7 days before parking a passenger car, and 28 days before regular use by trucks or heavy equipment. Cold weather slows curing dramatically — below 50°F, double the wait times and use blankets or accelerators. Hot weather speeds curing but causes plastic shrinkage cracks; keep the surface wet for the first 3 days and apply a curing compound. Never let fresh concrete freeze in the first 24 hours.
For sidewalks, patios, and shed floors, 2,500-3,000 psi (17-21 MPa) is sufficient. For residential driveways and garage floors, specify 3,500-4,000 psi (24-28 MPa) and request air entrainment if your climate freezes. For foundations and footings, 3,000-4,000 psi is standard. Suspended structural slabs, beams, and columns typically use 4,000-5,000 psi (28-35 MPa). High-rise columns and bridges may go to 6,000-10,000 psi. Higher PSI costs more per cubic yard but extends service life and resists freeze-thaw, deicing salts, and abrasion. Always specify both strength and slump (flowability) when ordering ready-mix.
The mix ratio is the proportion by volume of cement : sand : coarse aggregate. Common nominal mixes are 1:2:4 (M15, ≈15 MPa) for plain footings and mass concrete, 1:1.5:3 (M20, ≈20 MPa) for most reinforced slabs, columns and beams, and 1:1:2 (M25, ≈25 MPa) for heavier structural work. To convert a poured (wet) volume into dry materials, multiply by the 1.54 dry-volume bulking factor, then split by the ratio parts: for 1 m³ of M20, dry volume = 1.54 m³, cement = 1.54 × 1/5.5 = 0.28 m³ ≈ 403 kg ≈ 8 bags of 50 kg (rounded up to 9 for ordering), sand = 0.42 m³, aggregate = 0.84 m³. The water-cement ratio sets strength and workability: 0.4-0.5 for structural concrete, up to 0.6 for non-structural — lower water means higher strength. Use the Mix strength selector above to get this take-off automatically for any shape you calculate.
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