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CALCULATOR · Converters

Concrete Calculator

Estimate the cubic yards and cubic meters of concrete needed for a slab, rectangular footing, cylindrical column or stairs, with a configurable waste percentage and 80 lb / 60 lb bag estimates.

Show formula
Slab: L × W × thickness. Footing: L × W × depth. Column: π × (d / 2)² × height. Stairs: risers × riser height × tread depth × width (solid volume — does not subtract the open tread gap). All inputs converted to m then volume in m³; yd³ = m³ × (1/0.9144)³. Bag estimate assumes 80 lb = 0.60 ft³, 60 lb = 0.45 ft³ cured yield.

Method reviewed:Geometry: standard SI factors (1 ft = 0.3048 m, 1 yd³ = 0.764554857984 m³). Bag yields: manufacturer-stated 80 lb / 60 lb pre-mix yields reviewed against Quikrete and Sakrete data sheets.

Inputs

20
10
4
10

10% covers spills, over-excavation and small voids. Increase for pumped pours.

Planning tool only — not a structural engineering model. Assumes a perfect rectangular prism or cylinder, with no deduction for rebar, voids, over-excavation or formwork losses. For load-bearing footings, columns or slabs, consult a structural engineer or a ready-mix concrete supplier.

Result

Adjusted volume

Adjusted volume: 2.716 yd³

2.077 m³

Base volume
2.469 yd³

1.888 m³

Waste %
10%
80 lb bags
123

Assumes 80 lb = 0.60 ft³, 60 lb = 0.45 ft³ cured yield.

60 lb bags
163

Assumes 80 lb = 0.60 ft³, 60 lb = 0.45 ft³ cured yield.

Actual yield varies with mix, water ratio, aggregate size, and placement method — always round up.

  • Bag yield: 80 lb = 0.60 ft³, 60 lb = 0.45 ft³ after curing.Estimates assume an 80 lb bag yields 0.60 ft³ and a 60 lb bag 0.45 ft³ of cured concrete — the figures published by major pre-mix suppliers; actual yield varies with mix, aggregate and placement.
Show formula
Slab: L · W · thickness. Footing: L · W · depth. Column: π · (d / 2)² · height. Stairs: risers · riser height · tread · width. All inputs to m, then m³; yd³ = m³ · (1 / 0.9144)³.

Bag yield assumption

How the concrete calculation works

  1. Pick a shape — slab, rectangular footing, cylindrical column or stairs — and choose imperial or metric units.
  2. Enter the dimensions in their natural units. Thickness and diameter are in inches for imperial and centimetres for metric; lengths are in feet or metres.
  3. Read the adjusted volume (base + waste) in cubic metres and cubic yards, plus the bag count based on the 80 lb / 60 lb yield assumption on the page.

Frequently asked questions

Is this exact enough for structural work?

No. The calculator is a planning tool, not a structural engineering model. It assumes a rectangular prism or a perfect cylinder, with no deduction for reinforcement, voids, over-excavation or waste at the forms. For footings, columns or load-bearing slabs, a structural engineer or a ready-mix supplier's quote is the right reference.

How accurate is the bag estimate?

The 80 lb bag at 0.60 ft³ and 60 lb bag at 0.45 ft³ cured yield are the figures published by major pre-mix suppliers. Actual yield varies with mix, water ratio, aggregate size and how the concrete is placed (a wheelbarrow and a slab pour lose different amounts). Round up.

What does the waste percent cover?

The default 10% covers spillage, over-excavation, slab-edge loss and a small amount of unexpected voids. Increase it for hand-mixed or pumped pours where slump loss is harder to predict.

Examples

20 ft × 10 ft slab, 4 in thick.
20 × 10 × (4/12) = 66.67 ft³ ≈ 1.89 m³. With 10% waste: 2.08 m³. That is 123 × 80 lb bags at the stated yield.
A 12 in diameter, 8 ft tall column.
π × (0.5)² × 8 = 6.28 ft³ ≈ 0.18 m³. With 10% waste: 0.20 m³ — 12 × 80 lb bags.

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