Solve backwards
How big a slab will a yard of concrete pour?
- 3 yd³The example worked below
- Concrete CalculatorEvery figure is its own
You have
How much ready-mix concrete?
That is 3 yd³(2.3 m³). Worked by the Concrete Calculator at the settings below.
The settings it uses
- Slab Thickness
- 4 in
- Waste Factor (%)
- 10
What it will do
221 sq ft of slab
20.5 m²
One slab. Enough for a slab 14.9 × 14.9 ft at 4 in deep.
Or several. About 2 slabs of the size the Concrete Calculator opens on: a slab 10 × 10 ft at 4 in deep.
Check it forwards
- Slab Length
- 14.9 ft
- Slab Width
- 14.9 ft
- It asks for
- 3 yd³
- You have
- 3 yd³
The Concrete Calculator asks for 3 yd³ at that size.
If you had more, or less
Around your amount
Each worked by the Concrete Calculator at the same settings.
Half
1.5 yd³
110 sq ft
a slab 10.5 × 10.5 ft at 4 in deep
Yours
3 yd³
221 sq ft
a slab 14.9 × 14.9 ft at 4 in deep
Half as much again
4.5 yd³
331 sq ft
a slab 18.2 × 18.2 ft at 4 in deep
Double
6 yd³
442 sq ft
a slab 21 × 21 ft at 4 in deep
Common amounts
What each amount of ready-mix concrete covers
The sizes it is usually sold in, each worked by the Concrete Calculator at the settings above.
| You have | It covers | As one slab | Average slabs |
|---|---|---|---|
| 1 yd³(0.8 m³) | 73.6 sq ft(6.84 m²) | a slab 8.6 × 8.6 ft at 4 in deep | under 1 |
| 2 yd³(1.5 m³) | 147 sq ft(13.7 m²) | a slab 12.1 × 12.1 ft at 4 in deep | 1 |
| 3 yd³(2.3 m³) | 221 sq ft(20.5 m²) | a slab 14.9 × 14.9 ft at 4 in deep | 2 |
| 5 yd³(3.8 m³) | 368 sq ft(34.2 m²) | a slab 19.2 × 19.2 ft at 4 in deep | 3 |
| 10 yd³(7.6 m³) | 736 sq ft(68.4 m²) | a slab 27.1 × 27.1 ft at 4 in deep | 7 |
Four inches for a patio, six for a drive
Four inches, about 100 mm, is standard for a patio or walkway, and the calculator opens there; six inches, about 150 mm, is common for a driveway that carries vehicles. A cubic yard pours 81 square feet at 4 inches and 54 at 6 — so the same truck finishes a third less driveway than patio.
Ten per cent never reaches the forms
The calculator orders ten per cent over the geometry for spillage, an uneven subgrade and forming slop, because running short with concrete already mixed is serious. Read backwards, the same tenth comes off the load: three cubic yards pour a slab of about 2.7 yards' worth, not three.
The truck has its own rules
The volume is not an order quantity. Ready-mix is sold in fixed increments with a minimum load and short-load charges, and concrete left in the drum, chute or pump line is not counted. Thickened edges, footings and a base that dishes in the middle all take concrete the flat slab never shows.
How the answer is worked
Nothing here is a second formula. The Concrete Calculator runs forwards — a size in, a quantity out — and this page grows its own starting slab in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Concrete Calculator
runs it forwardsEstimate how much concrete a slab needs — in cubic yards or cubic metres, and as a count of premix bags.
Work out what to buy insteadSolve backwards
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Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much slab does 3 yd³ of ready-mix concrete cover?
- At the Concrete Calculator's own settings, 221 sq ft (20.5 m²) — a slab 14.9 × 14.9 ft at 4 in deep. That is about 2 slabs of the size the calculator opens on: a slab 10 × 10 ft at 4 in deep. Every figure follows the settings, which you can change in the calculator.
- How much slab does 2 m³ of ready-mix concrete cover?
- At the Concrete Calculator's own settings, 18.2 m² (196 sq ft) — a slab 4.3 × 4.3 m at 100 mm deep. That is about 2 slabs of the size the calculator opens on: a slab 3 × 3 m at 100 mm deep. Every figure follows the settings, which you can change in the calculator.
- How many square feet does a yard of concrete cover?
- At 4 inches thick a cubic yard covers 81 square feet (7.5 m²); at 6 inches, 54; at 3.5 inches, about 93. Allow ten per cent for spillage and an uneven base, and plan on about 74 square feet at 4 inches.
- How big a slab will a cubic metre of concrete pour?
- At 100 mm thick a cubic metre pours 10 m² (108 square feet), at 150 mm about 6.7 m². With the usual ten per cent for spillage and the base, plan on about 9 m² at 100 mm — a square about 3 metres a side.
- How many 80 lb bags make a yard of concrete?
- An 80 pound (36 kg) bag yields about 0.6 cubic feet (17 litres) mixed, so a cubic yard of 27 cubic feet takes 45 bags. Above a cubic yard or so, ready-mix is usually the sensible order; the concrete bag solver reads bags the same way this page reads a load.