Concrete volume calculator
Estimate slab concrete needs in cubic yards or cubic metres, plus bag counts.
What this calculator covers
Estimate how much concrete a rectangular slab needs before ordering ready-mix or bagged material. Choose imperial inputs (ft length/width, in depth → cubic yards) or metric inputs (m length/width, cm depth → cubic metres) so the order quantity matches the unit your supplier quotes.
The page focuses on practical takeoff math: unit conversion, prism volume, and final order quantity.
Frequently asked questions
- Which unit system should I pick?
- Pick the one your supplier quotes in. North American ready-mix and bagged concrete is sold in cubic yards, so imperial (ft/in → cubic yards) matches what you will hear on a delivery call. Outside the US, suppliers usually quote cubic metres, so metric (m/cm → cubic metres) is the natural fit. The math is identical either way — the calculator just converts internally and reports the order-ready volume in the unit you picked.
- Why do concrete suppliers quote volume in cubic yards rather than cubic feet?
- Ready-mix trucks and batch plants size loads in cubic yards because the quantities involved make cubic feet unwieldy — a standard residential pour can easily exceed 100 cubic feet. The calculator converts to cubic yards as the final order-ready unit for imperial inputs since that is what most US suppliers require for scheduling a delivery. Metric suppliers use cubic metres for the same practical reason.
- How thick should a typical concrete slab be?
- Slab thickness depends on the application. A 4-inch depth is common for residential driveways and patios, while structural slabs, heavy vehicle areas, and slabs on expansive soils may require more. Local building codes and soil conditions govern the minimum — verify requirements with a contractor or inspector before pouring.
- Does the volume estimate include any waste allowance?
- No. The result is the theoretical volume of the rectangular slab. It is common practice to order an additional 5–10% above the calculated volume to account for ground irregularities, spillage, and the difficulty of measuring the pour area exactly.
- Can I use this for non-rectangular shapes?
- Not directly. For L-shaped, circular, or irregularly shaped pours, break the area into rectangular sections, calculate volume for each, and add the results together. The concrete-bags calculator on this site uses the same rectangular slab approach.
Tool
Run the calculation
Result
RESULT · CONCRETE
â„–009
Primary result
1.48 yd³
A 12 ft by 10 ft slab at 4 in deep needs 1.48 cubic yards of concrete.
- Unit system
- Imperial
- Cubic feet
- 40.00
- Cubic yards
- 1.48 yd³
- Approx. 60 lb bags
- 89
Step-by-step solution
- 1.Convert the depth to feet: 4 in ÷ 12 = 0.3333 ft.
- 2.Multiply length × width × depth to get a volume that displays as 40.00 cubic feet.
- 3.Divide the exact cubic-foot volume by 27 to convert to 1.48 cubic yards.
Walkthrough
Visual walkthrough
Concrete ordering starts with a rectangular volume, then converts that volume into the unit suppliers use.
01
Convert slab depth into feet
4 ÷ 12 = 0.3333 ft
Length and width are already in feet, so depth has to match before volume math works.
02
Compute the slab volume
12 × 10 × 0.3333 = 40.00 ft³
A slab is a rectangular prism, so volume is length times width times depth, with the displayed cubic-foot figure rounded for readability.
03
Convert to order quantity
Most suppliers quote ready-mix in cubic yards, so the exact cubic-foot volume is divided by 27.
1.48 yd³ required