=AllInOneCalculator

Concrete Calculator

Estimate concrete volume for slabs, footings, walls, round columns, and stairs in cubic yards, cubic feet, and cubic meters — with bag counts and optional cost.

Order volume (with 10% waste)
1.63 yd³
44.0 ft³ · 1.25 m³
Volume without waste1.48 yd³ · 40.0 ft³ · 1.13 m³
80 lb bags74
60 lb bags98
40 lb bags147
Shape: Slab / wall / footing · Waste: 10%
Formula: V = L × W × T
Bag counts are rounded up. Ready-mix is commonly ordered in 1/4 yd³ increments — confirm with your supplier.
Results update as you type

What this calculator does

This concrete calculator handles slab/wall/footing rectangles, round columns and tube footings, and stair steps. It returns volume in cubic yards, cubic feet, and cubic meters, plus 40 lb, 60 lb, and 80 lb bag counts and an optional cost estimate. A configurable waste percentage is applied to bag counts and the ordering volume.

Formula

Slab / wall / footing: V_ft³ = length × width × thickness_ft

Column / round footing: V_ft³ = π × (diameter / 2)² × height_ft

Stairs: sum of each step's volume (run × width × rise/2 + run × width × prior rise for the platform behind each tread).

Conversions: V_yd³ = V_ft³ ÷ 27 · V_m³ = V_ft³ × 0.0283168

Bag count: bags = ⌈V_ft³ ÷ bag_yield × (1 + waste)⌉

Variable definitions

  • length / width / thickness — Slab dimensions — length and width in feet, thickness usually in inches (converted to feet by ÷ 12).
  • diameter / height — Column or tube footing diameter and height, in your chosen unit.
  • bag yield — Concrete from one bag: 0.30 ft³ for 40 lb, 0.45 ft³ for 60 lb, 0.60 ft³ for 80 lb.
  • waste — Extra ordered to allow for spillage and over-pour, as a decimal (0.10 for 10%).

Step-by-step calculation

  1. Pick the shape that matches your pour.
  2. Enter the dimensions in the units of your choice — the calculator converts everything to feet.
  3. Set the waste percentage (5–10% is typical).
  4. Optionally enter a price per cubic yard and per bag for a cost estimate.
  5. Order ready-mix by the cubic-yard figure, or bagged mix by the rounded-up bag count.

Worked example

Patio slab: 12 ft × 10 ft × 4 in, 10% waste.

  • Thickness in feet: 4 ÷ 12 = 0.333 ft
  • Cubic feet: 12 × 10 × 0.333 = 40 ft³
  • Cubic yards: 40 ÷ 27 = 1.48 yd³ (order ~1.63 yd³ with waste)
  • 80 lb bags: ⌈40 ÷ 0.60 × 1.10⌉ = 74 bags
  • 60 lb bags: 98 bags · 40 lb bags: 147 bags

How to use this calculator

  1. Choose the shape tab (slab/wall/footing, column/round, or stairs).
  2. Enter dimensions in your preferred units.
  3. Adjust the waste percentage if your pour is unusually complex.
  4. Enter ready-mix and bag prices for an itemized cost.

Common mistakes

  • Mixing units: thickness is often in inches while length and width are in feet — the calculator converts but double-check your inputs.
  • No waste factor: a pour that comes up short is far costlier than leftover concrete.
  • Rounding bags down: always round bag counts up to the next whole bag.

Frequently asked questions

›How do I calculate how much concrete I need?

Multiply length × width × thickness to get the volume in cubic feet (convert all dimensions to feet first), then divide by 27 to get cubic yards. For a 10 ft × 10 ft slab that's 4 inches thick: 10 × 10 × (4/12) = 33.33 cubic feet, or about 1.23 cubic yards.

›Should I add extra concrete for waste?

Yes. A 5%–10% waste factor is standard for slab pours; add 10–15% for awkward forms or first-time pours. The calculator lets you set the waste percentage.

›How many bags of concrete do I need?

An 80 lb bag yields ~0.60 cubic feet, a 60 lb bag ~0.45 cubic feet, and a 40 lb bag ~0.30 cubic feet. Divide total cubic feet by the bag yield and round up. The calculator shows all three counts.

›What is the difference between cubic feet and cubic yards?

1 cubic yard = 27 cubic feet. Ready-mix concrete is usually ordered in cubic yards; bagged mix is rated in cubic feet.

›How thick should a concrete slab be?

4 inches is typical for sidewalks, patios, and shed floors. 5–6 inches is common for driveways depending on load and freeze-thaw cycles.

›How do I calculate concrete for a round column or tube footing?

Volume = π × radius² × height. The Column / Round mode does this automatically — just enter the diameter and height.

›Can I estimate the cost of the concrete?

Yes. Enter the price per cubic yard (for ready-mix) or per bag, and the calculator multiplies by the volume or bag count to show a total.

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Last updated: June 22, 2026 · Checked against standard formulas and sample test cases. Bag yields use industry-standard published values (Quikrete / Sakrete equivalents). Confirm with your supplier.

Disclaimer: Material estimates should be verified before purchasing or building. Add a waste factor appropriate to your project.