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Concrete Calculator

Calculate the net concrete volume for a rectangular slab or pad, then add a practical waste allowance for spillage, uneven ground, and measurement variation.

Calculate Concrete to Order

Common planning allowances are often 5–10%, but site conditions may require more.

Order Volume = Length × Width × Thickness × (1 + Waste %)

A 5 m × 4 m slab at 10 cm thick has a net volume of 2.00 m³. With 7.5% waste, plan to order about 2.15 m³.

Measure the project carefully, use the effective product dimensions or coverage supplied by the manufacturer, add a realistic allowance, and round purchasing quantities up to saleable units.

Use this estimate before requesting quotations, comparing suppliers, preparing a budget, or checking whether delivered quantities match the planned project.

Do not mix units, use nominal dimensions where effective coverage is required, or treat a planning estimate as a structural specification.

Worked Example

A 5 m × 4 m slab at 10 cm thick has a net volume of 2.00 m³. With 7.5% waste, plan to order about 2.15 m³.

Buying tip: Round up to the supplier’s available pack, bag, sheet, can, truck, or batch size after confirming the product specification.

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When to Use It

  • Floor slabs and walkways
  • Equipment bases and pads
  • Footing volume checks
  • Supplier order comparisons
  • Budget preparation

How It Works

  • Measure the real project dimensions.
  • Enter effective product coverage and waste.
  • Review and round the result to purchasable quantities.

Common Mistakes

  • Entering thickness in metres instead of centimetres
  • Using plan dimensions before confirming formwork
  • Ignoring uneven excavation or spillage
  • Ordering without checking truck or mixer capacity

Materials and Tools to Compare

  • Concrete mixing tools
  • Wheelbarrows and buckets
  • Compaction equipment
  • Curing sheets or membrane

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Frequently Asked Questions

How much waste should I add to concrete?

A planning allowance of 5\u201310% is common for straightforward work, but difficult access, irregular excavation, pump lines, or uncertain measurements can require more.

Does this calculate cement, sand, and aggregate?

This page calculates concrete volume. Use the Cement Bags, Sand, and Gravel calculators for separate material estimates.

Can I use it for columns or circular footings?

This version is designed for rectangular slabs and pads. Use the dedicated column or foundation calculators for other shapes.

Why is thickness entered in centimetres?

Slab thickness is commonly measured in centimetres while length and width are measured in metres. The calculator converts thickness to metres internally.

Should I round concrete volume up?

Yes. Suppliers normally sell in practical batch or truck quantities, so round up after adding waste and confirm the minimum delivery quantity.

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