Does this concrete calculator work in metric?

Yes. Switch units to Metric to enter dimensions in metres and centimetres and see the result in cubic metres alongside cubic yards and cubic feet.

Concrete Volume & Bag Estimator

CONCRETE CALCULATOR

Q: How do I calculate how much concrete I need?

Measure length, width, and thickness in the same unit, multiply them for the volume, then convert to cubic yards by dividing cubic feet by 27. For round columns use pi times radius squared times height. Add about 10% extra for waste.

Q: How many 80 lb bags of concrete are in a cubic yard?

An 80 lb bag yields about 0.60 cubic feet. A cubic yard is 27 cubic feet, so you need about 45 bags of 80 lb concrete per cubic yard. For 60 lb bags it is 60 per yard and for 40 lb bags it is 90 per yard.

Q: How much concrete do I need for a 10x10 slab?

A 10 ft by 10 ft slab at 4 inches thick is about 33.3 cubic feet, or 1.23 cubic yards. With 10% waste allowance, order around 1.36 cubic yards, roughly 61 bags of 80 lb concrete.

Q: Should I add extra concrete for waste?

Yes. Allow 5 to 10% extra for spillage, over-excavation, and uneven ground. Ten percent is a safe default for small pours.

Q: Is it cheaper to use bags or ready-mix?

Bagged concrete suits small jobs but costs more per yard. Once you need more than about 1 cubic yard, around 45 bags of 80 lb concrete, ready-mix delivery is usually cheaper.

Work out exactly how much concrete you need. Enter your dimensions and this concrete calculator returns the volume in cubic yards, the number of 40, 60, or 80 lb bags, and an optional cost — for a slab, footing, column, or stairs.

Dimensions

INPUT

Units

Quantity

Waste / Spillage — 10%

Price / yd³ (optional)

Price / 80lb bag (opt.)

DETAIL — SLAB N.T.S.

Concrete RequiredSLAB

0.00yd³

= 0 ft³ · = 0 m³

Order ≈ 0.00 yd³ ready-mix

40 lb bags

60 lb bags

80 lb bags

Ready-mix cost: $0

Bagged (80lb) cost: $0

HOW MUCH CONCRETE DO I NEED?

Concrete is ordered by volume — in cubic yards (US) or cubic metres. This concrete calculator multiplies your dimensions to find that volume, adds a waste allowance, then converts it into the number of pre-mix bags or the amount of ready-mix to order.

How to use the concrete calculator

Pick the shape you're pouring: slab, footing, round column, or stairs.
Choose Imperial (ft / in) or Metric (m / cm) and enter your dimensions.
Set how many identical pours you need with Quantity, and add a waste allowance (10% is typical).
Read your volume in cubic yards, plus the bag count and optional cost.

The formulas

All dimensions are converted to a common unit before multiplying:

Slab / footing: volume = length × width × thickness
Round column: volume = π × (diameter ÷ 2)² × height
Stairs: volume = width × run × rise × [n × (n + 1) ÷ 2], for n steps
Then: cubic yards = cubic feet ÷ 27, and waste is added as × (1 + waste%).

How many bags of concrete in a cubic yard?

A cubic yard is 27 cubic feet. Each pre-mixed bag yields a fixed volume, so:

Bag size	Yield	Bags per yd³
80 lb (36 kg)	0.60 ft³	45 bags
60 lb (27 kg)	0.45 ft³	60 bags
40 lb (18 kg)	0.30 ft³	90 bags

Because bagged concrete gets expensive fast, ready-mix delivery is usually cheaper once you pass roughly 1 cubic yard (about 45 × 80 lb bags).

CONCRETE FAQ

How do I calculate how much concrete I need?

Measure the length, width, and thickness of the area in the same unit, multiply them to get the volume, then convert to cubic yards by dividing cubic feet by 27. For round columns use π × radius² × height. Add about 10% extra for spillage and uneven subgrade. This calculator does all of that automatically.

How many 80 lb bags of concrete are in a cubic yard?

An 80 lb bag of concrete yields about 0.60 cubic feet. A cubic yard is 27 cubic feet, so you need 27 ÷ 0.60 ≈ 45 bags of 80 lb concrete per cubic yard. For 60 lb bags it's 60 per yard, and for 40 lb bags it's 90 per yard.

How much concrete do I need for a 10x10 slab?

For a 10 ft × 10 ft slab at 4 inches thick: 10 × 10 × (4 ÷ 12) = 33.3 cubic feet, or about 1.23 cubic yards. With a 10% waste allowance, order around 1.36 cubic yards — roughly 61 bags of 80 lb concrete.

Should I add extra concrete for waste?

Yes. Allow 5–10% extra to cover spillage, over-excavation, and uneven ground. For small or awkward pours, 10% is a safe default. Running short mid-pour creates a cold joint, so it's better to slightly over-order.

Is it cheaper to use bags or ready-mix?

Bagged concrete is convenient for small jobs, but the per-yard cost is high. Once you need more than about 1 cubic yard (≈45 × 80 lb bags), ready-mix delivery is usually cheaper and far less labor.

Does this work in metric (cubic metres)?

Yes. Switch the units to Metric to enter dimensions in metres and centimetres; the calculator shows the result in cubic metres alongside cubic yards and cubic feet.