Concrete Calculator

About the Concrete Calculator

A concrete calculator estimates the volume of concrete needed for slabs, footings, columns, steps, and any other poured concrete element — in cubic yards (US) and cubic metres (metric) — along with the equivalent number of pre-mixed bags required. Ordering the right amount of ready-mix concrete is critical: concrete must be poured continuously for monolithic slabs, so a short order means stopping mid-pour (a structural disaster), while over-ordering wastes $100-150 per cubic yard and leaves you with hardened material to dispose of. Our free concrete calculator adds a recommended 10% overage for spillage, pump waste, and uneven subgrade, shows both ready-mix quantities and the number of 40-lb, 60-lb, or 80-lb bag equivalents for smaller pours, and includes a cost estimator based on current local ready-mix prices. It covers all common pour types: flat slabs (driveways, patios, sidewalks), rectangular footings, round columns, and circular sonotubes for deck posts.

How It Works

Volume formula for slabs: Volume (cubic yards) = Length (ft) x Width (ft) x Thickness (inches) / 324. The divisor 324 = 12 inches/foot x 27 cubic feet/cubic yard. Example: 10 ft x 20 ft driveway at 4-inch thickness: Volume = 10 x 20 x 4 / 324 = 800 / 324 = 2.47 cubic yards. With 10% overage: 2.72 cubic yards. At $150/yard delivered: approximately $408 for ready-mix. Bag equivalent: 1 cubic yard requires approximately 45 x 60-lb bags or 34 x 80-lb bags (each 80-lb bag yields 0.60 cubic feet = 0.022 cubic yards). Round column (sonotube): Volume = π x radius² x height / 27. An 8-inch diameter, 4-foot column: V = π x (0.333)² x 4 / 27 = π x 0.111 x 4 / 27 = 0.052 cubic yards = approximately 2.4 x 80-lb bags.

Tips & Best Practices

• ✓Minimum thickness guidelines: pedestrian patios and sidewalks need 4 inches; residential driveways 4-5 inches; commercial driveways and truck areas 6 inches; garage floors 4-6 inches with wire mesh or rebar reinforcement.
• ✓Ready-mix minimum order: most suppliers require a minimum 1 cubic yard order and charge a short-load fee for orders under 3-4 yards. For small pours, bags may be more economical despite the higher per-yard cost.
• ✓Concrete cures, not dries: strength develops through a chemical hydration process over 28 days. Keep new concrete moist for the first 7 days (cover with wet burlap or plastic sheeting) to achieve full design strength.
• ✓Temperature limits: do not pour concrete when air temperature is below 40°F (4°C) or above 90°F (32°C) without cold-weather or hot-weather admixtures. Extreme temperatures impair proper curing and reduce final strength.
• ✓Reinforcement: wire mesh (6x6, W1.4xW1.4) provides basic crack control; rebar (No. 3 at 18 inches on centre each way) provides structural strength. Use rebar for driveways, structural slabs, and footings.
• ✓Expansion joints: control joints should be cut every 8-12 feet in slabs to direct cracking along planned seams rather than randomly across the slab surface.
• ✓Standard concrete mix: residential flatwork typically uses 4,000 PSI mix with a 4-5 inch slump. Footings may use 3,000 PSI. Specify mix design when ordering ready-mix.
• ✓Pump truck surcharge: for pours over 50 feet from the truck or elevated pours, a concrete pump truck adds $500-1,500 to the project cost — include this in your budget and in the volume calculation (pump waste is approximately 0.25 cubic yards).

Who Uses This Calculator

DIY homeowners pouring driveways, patios, sidewalks, shed floors, and deck footings. General contractors estimating and ordering ready-mix for construction projects. Builders calculating bag quantities for small repairs and additions. Homeowners getting accurate material budgets before requesting contractor bids.