Concrete Calculator
Free slab concrete calculator — length, width, thickness, and waste into cubic yards and cubic meters. Same volume for a driveway or footing rectangle. Bags, Sonotubes, and UK m³ explained below.
This online concrete calculator estimates how much concrete you need for a rectangular slab (or any pour you can treat as L × W × thickness). It reports cubic feet, cubic yards with waste, and cubic meters for UK / ready-mix orders. Add waste because forms are uneven. It is not the Home Depot, CEMEX, Sakrete, Firth, or Concrete Network app — it is MeasureZone’s free volume tool.
Estimate only. Confirm yards, mix, and price with your ready-mix plant or bag yield with the manufacturer. Not affiliated with Home Depot, CEMEX, Sakrete, or Firth.
Concrete calculator formula
yd³ = (L × W × (inches ÷ 12)) ÷ 27, then × (1 + waste%). m³ = ft³ × 0.028316846592.
Cylinder (Sonotube / fence post): yd³ = π × r² × h ÷ 27, with r and h in feet. Steps: sum each tread/riser as its own rectangle, or use this slab tool per run. Materials quantities follow from volume; they are not a 1:2:3 mix designer.
How to use this concrete calculator
- Enter slab length and width in feet (driveway, patio, or footing as a rectangle).
- Enter thickness in inches (4 in is common for a slab; footings are thicker).
- Set waste % (10% is a typical start).
- Read cubic yards for ready-mix and cubic meters for a UK order. For bags, divide cubic feet by the yield printed on the bag.
About this calculator
Formula for concrete calculation: volume (ft³) = length (ft) × width (ft) × thickness (ft). Thickness in inches ÷ 12. Cubic yards = ft³ ÷ 27. Then multiply by (1 + waste%). How to figure a concrete calculator: that is the slab form above. Concrete calculator for square feet: area (ft²) × thickness (ft) = ft³. A 20×10 ft patio at 4 in is 200 × (4/12) = 66.67 ft³ ≈ 2.47 yd³ before waste.
Bag concrete calculator: divide cubic feet by the yield on the bag (Sakrete 80 lb is often about 0.60 ft³; 60 lb about 0.45 ft³). Ready mix / CEMEX-style orders are in cubic yards (US) or cubic metres (UK). Concrete calculator weight: normal concrete is about 150 lb/ft³ (≈ 4,050 lb/yd³) or about 2,400 kg/m³ — multiply volume by density for an estimate, not a weighbridge ticket.
Sonotube, fence post, and post-hole calculators use a cylinder, not this rectangle: ft³ = π × (diameter÷24)² × height(ft). Block walls and CMU are block count plus mortar, unless you are filling cores or pouring a solid wall (then use L × H × thickness). Mix ratio (1:2:3) and self-leveler coverage are mix design or bag charts — this tool is volume. Crushed concrete (recycled aggregate) still uses the same yd³. Price / cost = volume × local rate; we do not quote supplier prices.
Examples
Slab: 20×10 ft, 4 in, 10% waste
66.67 ft³ → 2.47 yd³; with waste about 2.71 yd³ (about 1.89 m³ before waste).
Driveway rectangle
Treat the pour as length × width × thickness. Irregular drives: split into rectangles and add the yards.
Footing as a long slab
A 20 ft footing, 2 ft wide, 12 in thick: 20 × 2 × 1 = 40 ft³ ≈ 1.48 yd³ before waste.
Slabs, driveways, walls, and bags
Concrete calculator for slab, driveway, wall, or footing: enter the rectangle. Block wall pours (solid or filled cores) still need volume; counting CMU is a separate takeoff. Quick bag check: ft³ ÷ 0.60 for typical 80 lb bags, then round up.
- US ready-mix: order cubic yards (this result, with waste)
- UK / many plants: cubic metres (already shown)
- 80 lb bag ≈ 0.60 ft³ yield (read the bag)
- Weight ≈ 150 lb per ft³ for normal-weight concrete
Posts, mix, cost, and what we are not
Fence post, post hole, Sonotube, and cylinder pours use πr²h. Self-leveling overlay is a thin slab (small thickness). Mix / ratio calculators proportion cement, sand, and stone; they do not replace a volume takeoff. Crushed concrete as fill still uses cubic yards of space to fill.
Not a priced quote (concrete calculator cost depends on your plant). Not Home Depot, CEMEX, Firth, Team Elmer’s, Quick Creek, or Concrete Network software. Not a phone-only app — bookmark this free page. Always confirm with your supplier before you pour.
FAQ
How to figure concrete calculator?+
Measure length and width in feet and thickness in inches. Volume ft³ = L × W × (inches ÷ 12). Yards = ft³ ÷ 27. Add waste. Example: 20×10 ft × 4 in = 66.67 ft³ ≈ 2.47 yd³; with 10% waste ≈ 2.71 yd³.
How much concrete do I need calculator?+
Use the form for a slab. For a post or Sonotube, compute cylinder volume (πr²h) then convert to yards. Order a little extra — short loads are expensive. Confirm with your ready-mix plant.
How much concrete calculator?+
This free concrete calculator answers “how much” in ft³, yd³, and m³. Bags = ft³ ÷ bag yield. Cost = yards × the price your yard quotes that day — not a Home Depot cart total.
How many bags of concrete do I need?+
Take cubic feet from the result. An 80 lb bag often yields about 0.60 ft³ (check Sakrete or your brand). 66.67 ft³ ÷ 0.60 ≈ 111 bags. Ready-mix is usually cheaper past a few dozen bags.
How do I calculate Sonotube or fence-post concrete?+
This slab tool is a rectangle. For a tube: radius in feet = diameter (in) ÷ 24. Volume ft³ = 3.1416 × r × r × height (ft). Then ÷ 27 for yards. A 12 in tube 4 ft high is about 0.12 yd³ before waste.
Is this the Home Depot or CEMEX concrete calculator?+
No. Home Depot, CEMEX, Firth, Sakrete, Concrete Network, and similar brands have their own pages. The cubic-yard formula is the same. This is MeasureZone’s free web calculator, not their software or app store listing.