Project Parameters
Instant Estimate
Order Quantity
Rounded up to the nearest quarter-yard.
Volume Including Waste
Equivalent 80 lb Bags
An 80 lb premix bag yields approximately 0.60 cubic feet.
Slab Surface Area
Estimates use standard building formulas. Verify with an on-site contractor.
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Guide
How to calculate concrete for a slab
Concrete suppliers quote ready-mix by the cubic yard. Convert slab thickness from inches to feet, calculate cubic feet, divide by 27, and add a practical overage.
Measure the form
Measure the inside length and width of the prepared form in feet.
Confirm thickness
Use the designed slab thickness. Many patios and walkways are 4 inches, but structural work may require more.
Include an overage
Add 5–10% for uneven subgrade, spillage, and variations in form dimensions.
Mathematics
Formulas used
Cubic Feet
Length (ft) × Width (ft) × Thickness (in) ÷ 12Converts all dimensions into a single cubic-foot volume.
Cubic Yards
Cubic Feet ÷ 27There are 27 cubic feet in one cubic yard.
Answers & FAQ
Frequently asked questions
How much concrete is needed for a 10x10 slab at 4 inches?▼
The base volume is about 1.23 cubic yards. With 10% overage, order roughly 1.5 cubic yards.
How many 80 lb concrete bags make one cubic yard?▼
Approximately 45 bags are needed for one cubic yard because each 80 lb bag yields about 0.60 cubic feet.
How much extra concrete should I order?▼
Five to ten percent is typical. Irregular excavation or complex forms may justify a larger allowance.
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