How to Calculate Concrete?

This concrete calculator helps you quickly estimate how much concrete you need for different shapes.

Step 1 – Choose the shape

You start off by selecting the shape that best fits your project:

Slab / floor – for driveways, house floors, patios, etc.

Wall: for concrete walls or retaining walls.

Footer / footing – for foundations under columns or walls.

Rectangular column: vertical concrete columns with a rectangular section.

Stairs – treats the stair flight like a solid inclined slab.

Cylindrical column – round columns.

Cylindrical tube-hollow cylinders, such as manholes or pipes (outside and inside diameter).

Curb / gutter / barrier – long narrow elements beside roads or pavements.

Once you pick a shape, the calculator shows only the fields needed for that shape, so you don't get confused with extra inputs.

Step 2 - Select your unit system

Next, you choose among:

Metric: meters (m) and centimeters (cm)

Imperial / US: feet (ft) and inches (in)

You select the system you are comfortable with, and all input boxes and labels will be updated automatically.

Step 3 - Enter the dimensions

For each shape you simply fill in the dimensions:

Examples of inputs per shape (metric):

Slab

Wall

Footing

Rectangular column

Stairs

Cylindrical column

Cylindrical tube

Curb / gutter

The calculator considers every shape as a 3D solid and calculates its volume using the appropriate formula behind the scene. If you have more than one identical section, you can also enter the number in “Number of identical sections” (for example, 5 columns of the same size).

Step 4 - How the calculator works in the background

It reads your shape, unit system and dimensions.

It calculates the volume of one section:

This formula calculates slabs, walls, footings, stairs, curbs, and rectangular columns by multiplying length × width × thickness/height.

For cylindrical columns, it uses the formula for cylinder volume:

π × radius² × height.

For the cylindrical tubes, it calculates the outer volume - inner volume to get the actual concrete volume.

It multiplies the volume per section × number of sections to get the total volume.

It converts this volume into:

Cubic meters (m³)

Cubic yards (yd³)

Cubic feet (ft³)

Given the volume in cubic feet, it estimates how many premix bags you may need:

40 lb bag ≈ 0.30 ft³

60 lb bag ≈ 0.45 ft³

80 lb bag ≈ 0.60 ft³

Next, it shows the bag counts rounded up, because in real life you cannot buy a fraction of a bag – and it’s always safer to have a bit extra.

A simple real-life example (slab)

Suppose you are going to pour a small slab for a backyard patio.

Let's say:

Shape: Slab / floor

Unit system: Metric

Length = 4 m

Width = 3 m

Thickness = 10 cm

Number of identical sections = 1

Step-by-step:

The calculator converts thickness to meters:

10 cm = 0.10 m

It calculates volume in cubic meters:

Volume = length × width × thickness

= 4 m × 3 m × 0.10 m

= 1.2 m³

It converts 1.2 m³ to cubic feet:

1 m³ ≈ 35.3147 ft³

So, 1.2 m³ ≈ 1.2 × 35.3147 ≈ 42.38 ft³

It converts volume to cubic yards:

1 yd³ = 27 ft³

So, 42.38 ÷ 27 ≈ 1.57 yd³

Now it estimates premix bags:

40 lb bags ≈ 42.38 ÷ 0.30 ≈ 141.27 → 142 bags

60 lb bags ≈ 42.38 ÷ 0.45 ≈ 94.18 → 95 bags

80 lb bags ≈ 42.38 ÷ 0.60 ≈ 70.63 → 71 bags

So on the result side you'll see something like:

Cubic meters: 1.20 m³

Cubic yards: 1.57 yd³

Cubic feet: 42.38 ft³

40 lb bags: 142

60 lb bags: 95

80 lb bags: 71

This gives you a clear idea of how much concrete to order or how many bags to buy.

Why this calculator is useful

Saves time on manual calculations

Supports many common shapes used on site

Works in both metric and imperial units

Gives concrete volume and bag estimates in one place

Helps avoid under-ordering (and delays) or over-ordering (and waste)

Whether you're a homeowner doing a DIY project or a contractor preparing a quick estimate, this tool makes planning your concrete job much easier and more reliable.