Concrete Calculator
A 10×10 ft × 4 in slab needs 1.36 cu yd of concrete (with waste) — about 65 bags of 80 lb mix or $180–$275 in ready-mix. Enter your slab size for an exact estimate.
Inputs
Estimate
- Cubic yards needed (+10% waste)Includes 10% waste for spillage, over-pour, and uneven sub-grade.5.43cu yd
- 80 lb bagsEach 80 lb bag yields ~0.6 cubic feet.245bags
- 60 lb bagsEach 60 lb bag yields ~0.45 cubic feet.326bags
- Ready-mix cost — low$706
- Ready-mix cost — high$1,086
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Try Remodel AI freeHow to calculate concrete needs
Concrete is measured in cubic yards (cu yd). One cubic yard = 27 cubic feet. To calculate the cubic yards needed, multiply slab length × width × thickness (all in feet), then divide by 27. Always add 10% waste for spillage and uneven sub-grade.
For DIY bag concrete: an 80 lb bag yields about 0.6 cubic feet; a 60 lb bag yields 0.45 cubic feet. A 4-inch slab measuring 10×10 ft needs about 1.4 cubic yards = 65 bags of 80 lb concrete. Most DIYers switch to ready-mix delivery above 1 cubic yard.
Ready-mix concrete is delivered by the truck and costs $130–$200 per cubic yard depending on region, with most suppliers requiring a minimum order of 1 cubic yard. Short-load fees may apply for orders under 3 cubic yards.
Formulas used
- Cubic yards
(length × width × thickness_feet) / 27 × 1.10Thickness in feet = inches ÷ 12. The ×1.10 adds standard 10% waste factor. - 80 lb bags
cubic_feet / 0.6Each 80 lb bag yields about 0.6 cubic feet of cured concrete. - 60 lb bags
cubic_feet / 0.45Each 60 lb bag yields about 0.45 cubic feet of cured concrete.
Frequently asked questions
How many 80 lb bags of concrete are in a cubic yard?+
About 45 bags of 80 lb concrete equal one cubic yard. For a typical 10×10 ft slab at 4 inches thick (1.23 cu yd), you'd need approximately 56 bags of 80 lb concrete.
How much concrete do I need for a 10×10 slab?+
A 10×10 ft slab at 4 inches thick needs 1.23 cubic yards of concrete (1.36 cu yd with 10% waste). That's about 65 bags of 80 lb concrete or 87 bags of 60 lb.
How thick should a concrete slab be?+
4 inches for residential patios and walkways. 5 inches for medium-duty pads. 6 inches for driveways, garages, and any slab supporting vehicles. 8+ inches for heavy machinery or commercial use.
How much does ready-mix concrete cost?+
Ready-mix concrete costs $130–$200 per cubic yard delivered. A 20×20 ft slab at 4 inches thick (about 5 cubic yards) costs $650–$1,000 for concrete alone, before formwork, rebar, and labor.
When is ready-mix cheaper than bags?+
Above 1 cubic yard, ready-mix is almost always cheaper. At 1 cubic yard, bags cost $250–$300 (45 bags × $5–$7 each). Ready-mix delivered costs $130–$200 plus a short-load fee of $50–$150.