Estimate concrete volume and materials before you order

Use this concrete calculator to estimate the material required for a slab, footing, round column or curb. Enter the finished dimensions, quantity and waste allowance, then review the concrete volume, wet weight, full bags, full truckloads and material cost.

The calculator uses metres for length and width, centimetres for depth or diameter, cubic metres for volume, litres for bag yield and kilograms per cubic metre for density. Results update automatically as the inputs change.

How to use the concrete calculator

1. Choose Slab, Footing, Column or Curb from the shape preset.
2. For a slab, footing or curb, enter the length and width in metres and the depth or thickness in centimetres. For a column, enter its diameter in centimetres and height in metres.
3. Enter the number of identical sections in Quantity.
4. Set a waste allowance from 0% to 50%.
5. Replace the ordering assumptions with supplier values where available: wet-concrete density, yield per bag, truck capacity and price per cubic metre.
6. Review the total concrete to order alongside the base volume, waste volume, wet weight, full bags, full truckloads and material-only cost.

If sections have different dimensions, calculate them separately and combine the order requirements. Measure the actual pour rather than relying only on nominal drawing dimensions.

How concrete volume is calculated

Slabs, footings and curbs use a rectangular-volume calculation. Because depth is entered in centimetres, the calculator divides it by 100 before multiplying:

Base volume = length × width × (depth ÷ 100) × quantity

Round columns use the area of a circle multiplied by height and quantity. The entered diameter is converted from centimetres to a radius in metres:

Base volume = π × (diameter ÷ 200)² × height × quantity

The selected waste percentage is then added:

Concrete to order = base volume × (1 + waste percentage ÷ 100)

The main volume result is shown to two decimal places. The calculator also shows the base volume and the extra volume attributed to waste.

How weight, bags, truckloads and cost are estimated

Estimated wet weight is the adjusted concrete volume multiplied by the entered density:

Estimated weight = concrete to order × density

The bag calculation converts cubic metres to litres, divides by the entered yield per bag and rounds up to a whole bag:

Full bags = round up(concrete to order × 1,000 ÷ bag yield)

Truckloads are calculated by dividing the adjusted volume by the entered truck capacity and rounding up to a whole load:

Full truckloads = round up(concrete to order ÷ truck capacity)

Material cost is the adjusted concrete volume multiplied by the entered price per cubic metre:

Estimated cost = concrete to order × price per m³

The cost result covers concrete material only. It does not automatically add delivery, short-load charges, pumping, reinforcement, formwork, excavation, labour, finishing, taxes, overhead or margin.

Worked example using the calculator defaults

The default slab is 5 m long, 4 m wide and 10 cm thick, with a quantity of 1 and a 10% waste allowance. Its base volume is 2 m³, and waste adds 0.2 m³, producing an order estimate of 2.20 m³.

With the default assumptions of 2,400 kg/m³ density, 12 L yield per bag, 8 m³ truck capacity and $150 per m³, the calculator shows:

• 5,280 kg estimated wet weight
• 184 full bags
• 1 full truckload
• $330.00 estimated material cost

These defaults are an example, not supplier specifications. Replace them with the values for the mix, packaging, delivery vehicle and price relevant to the project.

Choosing a waste allowance

A waste allowance accounts for the difference between ideal geometry and an actual pour. Uneven excavation, complex formwork, spillage, over-excavation and several small placements can all increase material use.

The calculator accepts a waste allowance from 0% to 50% and defaults to 10%. Do not treat the default as a universal recommendation. Review the project geometry and site conditions, then confirm the final order quantity with the supplier or contractor. Ordering too little can interrupt a continuous pour, while substantial over-ordering adds cost and disposal work.

Input limits and validation

For slabs, footings and curbs, length and width must each be greater than 0 and no more than 50 m; depth must be greater than 0 and no more than 300 cm. For columns, diameter must be greater than 0 and no more than 500 cm, and height must be greater than 0 and no more than 100 m.

The remaining accepted ranges are:

• Quantity: 1 to 50
• Waste allowance: 0% to 50%
• Concrete density: 1,000 to 3,500 kg/m³
• Yield per bag: 1 to 100 L
• Truck capacity: 0.5 to 25 m³
• Price: $0 to $1,000 per m³

When an input is outside these ranges, the calculator hides the results and asks you to check the inputs.

Measuring common concrete shapes

Slabs and footings

Measure length and width at several points when the form or excavation is not perfectly regular. Enter the designed concrete thickness or depth, not the depth of unrelated sub-base layers. Split stepped or irregular areas into simpler sections and add their requirements.

Columns

The column preset is for a round column. Measure the diameter carefully; the radius used in the circular formula is half the diameter. Calculate sections separately when a column changes diameter or shape along its height.

Curbs

The curb preset uses the same rectangular length × width × depth method as slabs and footings. Curved runs, transitions and complex profiles may need to be divided into smaller sections for a more useful estimate.

Limits of the estimate

Concrete estimates are only as reliable as the dimensions and assumptions entered. Actual yield can differ because of moisture, air content, batching, consolidation, ground conditions and product specifications. Material standards, densities, bag yields, supplier minimums and truck capacities also vary.

Check current product documentation and local requirements before purchasing. For structural work, confirm dimensions, mix specifications and reinforcement requirements with a qualified professional. This calculator is a planning aid, not engineering or safety advice.

Related calculators

Use the Cubic Yard Calculator for general volume conversion, the Square Footage Calculator for project area and the Excavation Calculator for the material to remove before a pour.

Frequently asked questions

Why are bags and truckloads rounded up?

Suppliers sell whole bags and deliveries are planned as whole loads. Rounding up avoids presenting a fractional package or truckload as an order quantity. Always check supplier minimums and available delivery sizes.

Should I use the default concrete density?

The default is 2,400 kg/m³. Use the density specified for the actual concrete mix when it is available, because mix design affects the estimated wet weight.

Why might a supplier estimate be different?

The supplier may use a different density, product yield, truck capacity, rounding method or waste allowance. Site measurements and mix specifications may also differ. Use current supplier data when placing the final order.

Can I use the estimated cost as a customer quote?

Use it as a starting point for material planning. A complete quote may also require delivery, equipment, labour, reinforcement, formwork, excavation, finishing, taxes, overhead and margin.