Concrete Calculator
Calculate concrete volume, weight, and material requirements for construction projects.
Project Details
Concrete Specifications
Reinforcement
Pricing
Concrete Volume
146.7 ft³
Total Project Cost
Materials + Labor
Cost per Sq Ft
Project cost density
Materials Cost
Concrete + Rebar
Labor Cost
10.9 hours
Project Summary
Project Guidelines
- • Allow 7 days for initial curing, 28 days for full strength
- • Keep concrete moist during curing process
- • Order concrete early morning for best workability
- • Have all tools and crew ready before delivery
- • Check weather conditions before pouring
How it works
A concrete calculator finds the volume of concrete a slab, footing, or column needs. You multiply length by width by thickness to get cubic feet, then convert to cubic yards (the unit concrete is sold in) by dividing by 27.
Concrete volume
Cubic feet = length × width × thickness Cubic yards = cubic feet ÷ 27
- length, width
- slab dimensions in feet
- thickness
- depth in feet (4 in = 0.333 ft)
Worked example
- Slab 10 ft × 10 ft
- 4 inches thick = 0.333 ft
- Cubic feet = 10 × 10 × 0.333 = 33.3
- Cubic yards = 33.3 ÷ 27
≈ 1.23 cubic yards — order ~1.35 yd³ to allow for waste.
Good to know
- Add about 5–10% for spillage, uneven subgrade, and over-excavation.
- Convert the thickness to feet first (inches ÷ 12) before multiplying.
- Ready-mix is sold by the cubic yard; bagged concrete lists how many bags make a cubic foot.
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Frequently Asked Questions
How do I calculate how much concrete I need?
Multiply length × width × thickness (all in feet) to get cubic feet, then divide by 27 for cubic yards — the unit ready-mix is sold in. A 10 × 10 ft slab at 4 inches (0.33 ft) thick is about 33 cubic feet, or 1.2 cubic yards.
How many bags of concrete make a cubic yard?
About 45 80-lb bags or 60 60-lb bags per cubic yard — an 80-lb bag yields roughly 0.6 cubic feet. For anything much over a yard, truck-delivered ready-mix is usually cheaper and far less work.
How thick should a concrete slab be?
Patios and walkways are typically poured at 4 inches; driveways at 5-6 inches for regular vehicles. Thickness drives volume more than any other input, so decide it before ordering.
How much extra concrete should I order?
Add 5-10% for simple pours and 10-15% where the subgrade is uneven or forms are complex — running short mid-pour creates a weak cold joint.
When are permits required?
Structural slabs, footings, and work tied to buildings usually need permits; small patios and walkways often don't. Rules vary widely — check with your local building department.
How to estimate timeline?
Research typical durations, add buffer for weather/delays, consider drying times, and be realistic about work hours.