Construction · Volume · Bags
Concrete
Calculator
Estimate concrete volume, bags needed, mix ratios, and total cost for slabs, footings, columns, stairs, and round slabs. Supports imperial and metric units.
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Cubic Yards
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Bags Needed
Slab
Shape
🟫 Concrete Slab
Bag Size
40
lb bag
0.011 yd³
60
lb bag
0.017 yd³
80
lb bag
0.022 yd³
Settings
%
Typical Mix Ratio (Cement : Sand : Aggregate)
Volume Needed
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cubic yards
Cubic Feet
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Cubic Meters
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Shape Preview
Volume (yd³)
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Bags Needed
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Est. Cost
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w/ Waste
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Concrete Estimate
How to Calculate Concrete Volume
Concrete volume calculations depend on the shape you're filling. For slabs and footings, multiply length × width × thickness. Convert inches to feet first (divide by 12), then convert cubic feet to cubic yards (divide by 27).
Key Formulas
Slab: Volume = Length × Width × Thickness
Footing: Volume = Length × Width × Depth
Column: Volume = π × (Diameter/2)² × Height
Round: Volume = π × Radius² × Thickness
Convert: in → ft (÷ 12) | ft³ → yd³ (÷ 27) | yd³ → m³ (× 0.7646)
Bags per yd³: 40lb bag ≈ 0.011 yd³ → ~90 bags/yd³
60lb bag ≈ 0.017 yd³ → ~60 bags/yd³
80lb bag ≈ 0.022 yd³ → ~45 bags/yd³
Always add 5–10% waste for spills and overages.
How many bags of concrete do I need for a 10×10 slab?
A 10×10 foot slab at 4 inches thick = 10 × 10 × (4/12) = 33.33 cubic feet = 33.33/27 = 1.23 cubic yards. At 80lb bags (0.022 yd³ each): 1.23/0.022 ≈ 56 bags. Add 10% waste: ~62 bags. At 4 inches thick, you'd typically also consider ordering ready-mix concrete for slabs over 1 cubic yard — it's more cost-effective and results in a better, more uniform mix than hand-mixing many bags.
What is the standard concrete mix ratio?
The most common mix for general construction is 1:2:3 (cement:sand:aggregate) by volume, producing approximately 3000 PSI concrete. For stronger concrete: 1:1.5:3 gives ~3500 PSI (good for driveways). 1:1:2 gives ~4000 PSI (structural applications). For footings and foundations, 3000–3500 PSI is typical. Pre-mixed bags already contain the correct proportions — just add water per the bag instructions, typically about 3 quarts per 80lb bag.
When should I use ready-mix vs bag concrete?
Bag concrete (Quikrete, Sakrete) is best for small projects under 1 cubic yard — footings, fence posts, steps, small slabs. Ready-mix (truck delivery) is better for larger pours — more consistent, stronger, and cheaper per cubic yard for big jobs. Ready-mix has a minimum order (usually 1 cubic yard) and a delivery fee. If you need more than 50–60 bags, ready-mix is usually more cost-effective. Ready-mix also allows custom PSI ratings, fiber reinforcement, and additives for specific conditions.
How thick should a concrete slab be?
Recommended thicknesses: Walkways/paths: 4 inches. Residential driveways: 4–6 inches (6 inches for trucks/heavy vehicles). Patios and floors: 4 inches minimum. Garage floors: 4–6 inches. Structural slabs: engineer-specified, typically 6–10 inches. The thickness depends on the load it needs to support and the subgrade conditions. Always use rebar or wire mesh reinforcement in slabs over 4 feet wide to control cracking.