Concrete Calculator

Multiply length × width × depth to get cubic feet, then divide by 27 for cubic yards. For a 10×10 ft slab that's 4 inches thick: 10 × 10 × 0.33 = 33 cubic feet ÷ 27 = 1.22 cubic yards. Always add 10% extra for waste, spillage, and uneven ground. One cubic yard covers about 80 square feet at 4 inches thick.

Approximately 45 bags of 80-lb concrete, 60 bags of 60-lb concrete, or 90 bags of 40-lb concrete per cubic yard. Pre-mixed bags are convenient for small projects under 1 cubic yard. For larger projects (2+ cubic yards), ordering ready-mix concrete delivered by truck is more economical—around $125-150 per cubic yard vs. $5-7 per 80-lb bag.

The standard mix ratio is 1:2:3 (1 part cement : 2 parts sand : 3 parts gravel) by volume, with about 0.5 parts water. For stronger concrete (4000+ PSI), use 1:1.5:3. Pre-mixed bags already have the correct ratios. For DIY mixing, one 94-lb bag of Portland cement + 2 cubic feet sand + 3 cubic feet gravel + 4.5 gallons water makes approximately 0.17 cubic yards.

Standard residential slabs: 4 inches for patios, walkways, and shed floors. Driveways: 5-6 inches (6 inches for heavy vehicles). Garage floors: 4-6 inches with proper base. Foundation footings: typically 8-12 inches deep, extending below frost line. Always pour over 4-6 inches of compacted gravel base. Reinforce with rebar or wire mesh for slabs over 4 inches.

Concrete reaches 70% strength in 7 days and full strength (typically 4000 PSI) in 28 days. Wait 24-48 hours before walking on it, 7 days for light vehicle traffic, and 28 days for heavy loads. Keep concrete moist during the first 7 days for optimal curing—cover with plastic or spray water 2-3 times daily. Hot weather accelerates but weakens curing; cold weather below 50°F significantly slows it.